7/4/2026 at 7:13:29 AM
I really wish a Apple or another major OEM would integrate CO2 monitor into watches or smartphones. Suddenly, everybody would be aware of the CO2 level in the room, get alerts, etc. and the problem will just solve itself.There are so many rooms, classrooms, movie theaters and other places with poor ventilation where you just feel dizzy, or fall asleep, not knowing it was just due to lower oxygen levels in your blood. Raising awareness is the only real solution.
by gpt5
7/4/2026 at 3:43:18 PM
> I really wish a Apple or another major OEM would integrate CO2 monitor into watches or smartphonesCO2 levels are locally elevated in the area where you exhale. Someone sitting at a desk with their hands on a keyboard exhaling through their nose would be producing a directed stream of elevated CO2 straight at the sensor on their wrist. Same thing if someone puts their phone on their desk.
Even with the IKEA and other cheap sensors that are becoming popular, there is a learning curve where users discover that putting it on their desk right in front of where they’re breathing produces higher numbers than having it even 5 feet away.
The false positives from having a CO2 sensor that close to everyone’s face would be causing unnecessary alarm all over.
> There are so many rooms, classrooms, movie theaters and other places with poor ventilation where you just feel dizzy, or fall asleep, not knowing it was just due to lower oxygen levels in your blood. Raising awareness is the only real solution.
If someone is falling asleep in this many different places I would suspect undiagnosed sleep apnea or another condition first and foremost. Spaces like movie theaters have very high volumes of air due to their size and commercial building HVAC has much higher standards for air circulation than even your home. If someone was falling asleep in so many different places then the most likely common theme is that person and it should be checked out!
This is another reason why putting CO2 sensors on everyone’s wrists would be a mistake: It would start getting blamed for every vague condition people experience. This has already happened with wrist-worn heart rate monitors. My friends in the medical field see people all the time who come in with vague complaints and they’ve self diagnosed as being related to their heart because they can see their heart rate now.
You also have the wrong idea about what elevated CO2 does. It doesn’t reduce the oxygen levels in your blood. It makes it more difficult for your body to expel CO2, which can produce subtle changes in many processes.
by Aurornis
7/4/2026 at 3:48:23 PM
> CO2 levels are locally elevated in the area where you exhale.That's the same area we inhale from... Wouldn't be right to measure there then? It's not like we're interested in the amount of CO2 on the ground (in this discussion)
by riquito
7/4/2026 at 3:53:13 PM
No, because the studies that establish the levels correlated with cognitive changes use ambient CO2 levels. Not with a stream of air directed, maybe, from your nose to your wrist.It is not possible to come up with a different baseline for wrist-worn monitors because the measurements could change significantly based on even small factors like the position of the wrist or smartphone.
by Aurornis
7/4/2026 at 11:32:01 PM
That makes sense to me. There's a causal link between ambient air CO2 levels and cognitive changes, but the air in front of your face, which you breathe, doesn't play a role...A lack of direct study might make "in front of your face" numbers harder to interpret in absolutes, but relatively speaking I do think that's the number which matters more. Whole-room analysis is just a proxy for the air in front of your face.
by hansvm
7/4/2026 at 11:29:17 PM
Presumably after a month or so of being worn during the day and taken off at night (when the breathing doesn't apply -- and the device knows this), the device could deduce what the influence of the wearer is.by popalchemist
7/5/2026 at 6:47:29 AM
Exactly!I installed a CO2 monitor at home, which reminds me of ventilation in winter when I keep windows closed and heating on.
by jason1cho
7/5/2026 at 9:12:37 AM
Wouldn’t it still be useful because you could look at changes in the measurement? E.g. if I can’t draw any conclusions when my phone says 800 at the start of a meeting because it might be where I’m breathing, but an hour later in the same place it says 2500 couldn’t I conclude we need to take a break and let the room air out?by tzs
7/4/2026 at 3:49:13 PM
The air infront of you IS the air you breed in, why shouldn’t it be measured?by cotwo
7/4/2026 at 3:54:35 PM
Because the thresholds everyone gets from the studies were not measured in that location.It would be like the weather station telling you it was 160 degrees outside because they put their thermal sensor on the asphalt, but you wanted to know the air temperature.
by Aurornis
7/4/2026 at 4:08:42 PM
Or your watch telling you the room is 98 degrees because it's only ever measuring your body temperatureby BobaFloutist
7/4/2026 at 4:19:00 PM
That’s a much better example. Thanksby Aurornis
7/4/2026 at 6:45:53 PM
98F = 36.6Cby mito88
7/4/2026 at 7:36:36 PM
Mostly agreed but with that much data couldn't we easily have an adjusted CO2 number for local sensors ?I would imagine it's still relative unlike temperature on the wrist (which is too affected by body temp)
by Melatonic
7/4/2026 at 6:56:00 PM
CO2 does not stream out when you exhale like a fluid. It’s a gas. It dissipates quite immediately and behaves as all gases do - it expands to fill its container via something like Brownian Motion.by avazhi
7/4/2026 at 7:07:22 PM
Dissipation does not happen instantly.I’ve done development on products with CO2 sensors and I’ve spent a lot of time with them on my desk right in front of me and also off to the side. Readings right in front of me are predictably higher.
You can breathe into a CO2 sensor 18 inches from your mouth and watch the values spike upward.
by Aurornis
7/4/2026 at 7:17:41 PM
I generally have fans around, but I too use a CO2 detector in my home and have tested it in various places and situations. CO2 concentrations are not as localised as you are making them out to be. If they are elevated in front of my face, for example, I can also similar numbers just above and slightly behind my head. If you go outside and do it, you’ll be surprised that the number doesn’t move really change at all when at arms’ length. Airflow is really everything here.And, spoiler alert: if the entire area in front of you has an increased CO2 concentration, then your environment has an increased CO2 concentration. That’s the entire point.
Suffice to say I disagree strongly with both the argument that this would lead to hugely erroneous readings and also with the notion that people would panic.
by avazhi
7/4/2026 at 8:45:57 PM
> And, spoiler alert: if the entire area in front of you has an increased CO2 concentration, then your environment has an increased CO2 concentration. That’s the entire point.I don’t think you’re reading the discussion: The CO2 thresholds that people use are based upon ambient air.
The closer the measurement to your mouth, the higher the reading will be. It should be apparent why putting the sensor directly in front of your mouth will register higher numbers than having it across the room.
CO2 does not instantly diffuse throughout a space. If it did, it would be sufficient to have only very small air leakage in a space for the CO2 to diffuse out of it very rapidly
by Aurornis
7/4/2026 at 7:16:23 PM
Actually what you exhale is a fluid.The CO2 content is a single chemical species within a mixed gas. Any air currents will cause mixing. Otherwise it undergoes diffusion which is actually a fairly slow process, although much faster in gases than in liquids.
by fc417fc802
7/4/2026 at 11:44:24 AM
> There are so many rooms, classrooms, movie theaters and other places with poor ventilation where you just feel dizzy, or fall asleep, not knowing it was just due to lower oxygen levels in your blood. Raising awareness is the only real solution.Not wrong, but it is perhaps worth noting that there are already standards for proper ventilation. Generally you're looking at 5–10 cfm/person (2.5-5 L/s), depending on the facility and purpose of the room; see Table 6.2.2.1 in ASHRAE Standard 62.1 for the US:
* https://www.ashrae.org/file%20library/technical%20resources/...
Maybe set up a monitor, but if the room/facility has recently been renovated and meets modern (>2013) building codes, this 'should' have already been taken into account.
by throw0101a
7/4/2026 at 1:09:37 PM
Should…Whenever I travel, I bring a CO2 meter with me. It’s amazing how often the air is bad. Often in unexpected places. My meter hit 3100 in an uber once. I didn’t even notice until I got to my hotel room and looked at the data log. It was a fresh, hot day outside. The uber had windows closed and AC on. I bet he had no idea - but he was driving with significant cognitive impairment. Takeoff and landing in planes are always the worst. If you get sleepy as the plane is taking off, it’s not you. The plane’s ventilation doesn’t work properly when the plane is stationary. So before a plane is in the air, they often hit 2500.
by josephg
7/5/2026 at 2:04:34 AM
He’s not driving with significant cognitive impairment. Submarines and the ISS routinely operate at 5000 ppm. 60 years of studies and almost a century of operating submarines has shown no impairment at 5000 ppm.Then all of the sudden Satish 2012 comes along and shows serious cognitive impairment at 1000 ppm. The only studies that have replicated this involved Satish. Studies without Satish as a coauthor fail to replicate their findings.
If you think about it for a second, the levels of impairment Satish shows don’t make sense at all. You’d expect to see differences on SAT scores of hundreds of points between test centers with good ventilation and bad. You’d expect to see massive differences between regions where AC is more or less common. Or even between seasons.
by sarchertech
7/4/2026 at 11:01:01 PM
Cars have a "make the air bad" button, the recirculation button. Some people always have it on. I wonder if it's a factor in road rage.by jerlam
7/5/2026 at 6:13:51 AM
Sounds like you need to change your cabin filter.by fingerlocks
7/5/2026 at 12:06:48 PM
I think the 'make bad air' part, is that it allows carbon dioxide levels to build up...not that the air is unpleasant to the senses to breathe.by dnemmers
7/5/2026 at 6:34:18 AM
Perhaps a lot of people should change their cabin filters.Air quality should be good everywhere. But its not. You can't tell if you don't measure it.
by josephg
7/4/2026 at 11:33:56 PM
Interesting. I can barely stay awake in typical commercial planes, and I always attributed it to the lower partial oxygen pressure.by hansvm
7/4/2026 at 1:29:29 PM
When was the last time you had that sensor calibrated properly with a can of test gas and a multimeter?by quickthrowman
7/4/2026 at 1:36:26 PM
Take it outside, as long as it measures 400-450 it's probably good.Metrology calibration is necessary if you want accuracy better than 10%, but most of us don't care at all about that, instead we care about increments of 200ppm or more.
by colechristensen
7/4/2026 at 2:50:52 PM
Haha yes. 400-450ppm is fine. We’re doing just fine here. Everything is okay.by jameshart
7/4/2026 at 3:32:50 PM
The comment was about the accuracy of the sensor, not about raising CO2 levels across the globe.by jaapz
7/4/2026 at 5:31:07 PM
Sure. It just draws attention to the fact that a throwaway piece of advice for checking calibration of a CO2 sensor is ‘it should read 400-450ppm outside’ when a few short decades ago that advice would have been ‘it should read 300-350ppm outside’.It’s like if someone said ‘you can check if your chatbot’s news feed is complete and up to date by asking it for ‘recent mass shootings’. There should be two or three in the past seven days’. It’s true and a valid methodology but holy crap does it say something dark about where we are.
by jameshart
7/4/2026 at 8:47:49 PM
[flagged]by colechristensen
7/4/2026 at 11:04:47 PM
450 ppm is fine. It can go a lot higher and the world will only benefit from the increased plant growth. You do want faster plant growth to compensate for ongoing desertification, right?by youarenaive343
7/4/2026 at 11:57:07 PM
If faster plant growth were the only side effect you might have a point here.Boy, it sure has been hot this month, though.
by jameshart
7/5/2026 at 10:12:15 AM
Nice baitby squibonpig
7/4/2026 at 2:45:59 PM
Local factors can make your CO2 fluctuate by 200ppm. If you're near a busy road with not a lot of wind 600 ppm is possible. But it's not that important if you open your window at 1000 ppm or 1200 ppm.by ShinyLeftPad
7/4/2026 at 12:48:30 PM
Building codes that address this are wonderful, however:- Plenty of people live or work in older buildings, where are not up to standard. For example: my office probably violates the air quality sensibilities of the Victorian era, which is when it was originally built.
- Equipment breaks down, isn't operated properly, or wasn't installed correctly. Having monitors that measure air quality is an extra check. While you may not be able to get direct action upon a consumer sensor, it can help you push for action.
I've been in buildings of varying quality over the years. I've seen how it takes time to get people in to do air quality testing. Heck, I saw the government claim that the air quality was acceptable in schools during the pandemic because the schools had passive ventilation systems. That meant they could open windows. (To be fair, the air quality in most of those buildings was probably fine since that was how the buildings were designed. That said, such standards make it easy for some buildings to slip through the cracks.)
So yeah, sensors to the people!
by II2II
7/4/2026 at 9:37:04 PM
And let's not forget unscrupulous building owners/renters who will not employ the at least 10% fresh air intake rule on their HVAC system. This fresh air is outside air temperature, so their system has to change it's temp according to the thermostat setting, which costs money.by bloomingeek
7/4/2026 at 12:51:14 PM
This is correct, but there's still a lot of opportunity to do better.I've been involved with the build out of several office spaces in new and old buildings. We always took this sort of thing seriously and measured each room independently for a week (many at a time) ensuring we accounted for periods of high occupancy.
This let us tune the HVAC systems to operate more efficiently, ensuring comfortable temperatures and air circulation. Every time I've seen this done there were structural deficiencies that required remediation, some times it meant adjusting duct work.
Most modern office buildings are designed to be a platform for constructing spaces, as spaces usually evolve and change between leases and tenants. They're designed to accommodate this sort of thing.
However I've found that no build out nails this the first time. It's very hard! Often times things look fine but once you get people in the space things change drastically. It requires time and effort to address.
Several of my offices had such good air that I'd prefer being there over pretty much anywhere else -- even outside on poor AQI days.
I've also found that a lot of offices don't do any of this and their air quality is noticeably poor. And lastly I've found that the oldest buildings, including schools -- and I'm talking really old -- have very good air because they are so incredibly leaky. They're usually harder to cool and heat, though.
by xyzzy_plugh
7/4/2026 at 12:31:41 PM
I think modern domestic houses its the opposite. At least in Netherlands insulation is such a strong focus, due to climate change I think, that modern appartments have terrible ventilationby wouldbecouldbe
7/4/2026 at 12:44:11 PM
Stayed at a beautiful new house in Finland, with five people instead of the usual two, the CO2 detector intermittently went off while we were sleeping. Which the hosts assured us was a faulty detector. They also spoke to how extremely energy efficient the house was, to us it seemed like there wasn't enough ventilation, to improve the insulation. Against their wishes, I slept with all windows fully cracked, which was only ~2 inches due to the "efficient" design.by hydevito
7/4/2026 at 12:46:58 PM
This was probably CO not CO2? A CO2 monitor doesn't "go off", it just silently reports. CO would go off because it's deadly to have a CO leak.by pieterhg
7/4/2026 at 6:58:59 PM
My portable CO2 monitor goes off. You can set a levels of warning on the aranet. It is a very quiet, non-disruptive alarm, but an alarm nonetheless.I agree with OP. I don't always carry it along, but it has been a massive boost to my productivity.
by 317070
7/4/2026 at 5:59:45 PM
Poor ventilation is mostly an issue in homes built or renovated in the 1970s, when the oil crisis led to ill-considered efforts to save energy. New homes typically achieve energy efficiency by using heat pumps in the ventilation system.by jltsiren
7/4/2026 at 12:45:39 PM
How modern? We built or house in Belgium in 2016, and it was completely sealed, very well insulated, but the air quality was good because we had mechanical ventilation. Clean air blown in, stale air extracted which then went through a heat exchanger.The only issue this house had was it overheated. We had glass facing south. Even in winter it instantly became too hot.
by OptionOfT
7/4/2026 at 2:14:02 PM
> I think modern domestic houses its the opposite. At least in Netherlands insulation is such a strong focus, due to climate change I think, that modern appartments have terrible ventilationThe link I pointed to is all about ventilation, so just because people ignored an important component of building science, and focused on one aspect, does not invalidate it.
And while climate change is important and using efficiency to deal with it is useful, the thermal control layer is actually the least important of the four:
* https://buildingscience.com/documents/insights/bsi-001-the-p...
'Bulk' water (precipitation) and moisture can cause deterioration of the building materials (rot, crumbling), and also mold, which has its own health effects. Leaky houses can often blow conditioned air at much faster rates than thermal leakage.
by throw0101a
7/4/2026 at 12:42:15 PM
A friend of mine recently moved to a modern apartment, built only a few years ago to a very high isolation standard (Germany). I stayed over night and slept on his couch, the air got really really dry and stuffy. It was really uncomfortable.by avhception
7/4/2026 at 12:57:22 PM
Heat recovery ventilation is the answer to this. You also get the benefit of being able to filter it.by HPsquared
7/4/2026 at 2:16:24 PM
Energy recovery ventilation is the answer to this.HRVs only deal with temperature, but then you have humidity that is non-controlled: moisture coming in during the summer, and getting vented out in the winter (too-dry air coming in).
ERVs handle both.
by throw0101a
7/4/2026 at 9:24:04 AM
I think the issue is that the common tech requires sensors in an air-chamber. E.g. NDIR works by firing IR at a frequency that is absorbed by CO2. A sensor on the other side either measures the amount of IR light that got through (optical NDIR) or pressure/sound waves (photoacoustic NDIR). I guess that it's hard to use any existing sensors, because they are relatively large and probably water could easily get into the chamber.Would be extremely cool if Apple, Samsung, and others can crack this, though I think they'd have done it already if it was easy.
by microtonal
7/4/2026 at 9:50:16 AM
Oxygen sensors used in car catalyst systems use a different effect based on electrochemistry. I see no reason that couldn't be minuaritized to grain-of-sand size.The question is if oxygen levels are as good an indicator as CO2 levels... I suspect not.
by londons_explore
7/4/2026 at 11:17:52 AM
Based on numbers, O2 concentration is probably not a good indicator.Clean air contains about 20.9% O2 and 0.04% CO2. At 2000 ppm CO2, which according to the author is bad enough to impair judgement, that's 0.2% CO2, it that CO2 is the result of respiration, it means that about 0.2% O2 was consumed, so that's a drop from 20.9% to 20.7%, a very small difference. 20.7% is not low enough to have a significant effect, the CO2 itself is the problem, not the drop in O2. And using O2 concentration as a proxy for CO2 doesn't look reliable to me: the difference is small and other things, like humidity can affect O2 concentration.
As for the sensor, O2 sensor in cars compare the O2 concentration between the outside air and exhaust gases, it needs outside air as a reference, but what you are measuring is the outside air itself, you don't have that reference.
by GuB-42
7/4/2026 at 12:48:06 PM
>that's 0.2% CO2, it that CO2 is the result of respiration, it means that about 0.2% O2 was consumed,I dont know anything about human respiration, but I know a little about chemistry and theres no reason to assume this is true. Basic stoichiometry.
According to a random article on the internet[1], nominal co2 production is 80% of oxygen consumption.
Your point appears broadly correct, just wanted to point out some faulty reasoning that could lead to incorrect results in the future.
[1] https://societymechanicalventilation.org/wp-content/uploads/...
by kryogen1c
7/4/2026 at 1:12:56 PM
CO2 concentration doesn't start at zero, and by coincidence, if CO2 production is 80% of oxygen consumption, consuming 0.2% oxygen results in 0.16% CO2, add it to the base 0.04% and you get 0.2%.by GuB-42
7/4/2026 at 12:57:12 PM
> O2 sensor in cars compare the O2 concentration between the outside air and exhaust gases, it needs outside air as a referenceSource?
by jmb99
7/4/2026 at 1:30:55 PM
https://en.wikipedia.org/wiki/Oxygen_sensor#Automotive_appli...It looks that some O2 sensors that don't require a reference have been used (titania sensors) but even though they have some advantages, they are less precise and mostly obsolete.
by GuB-42
7/4/2026 at 1:08:42 PM
I had a project miniaturizing nasa tech for detecting hypoxia with o2 and CO2 sensors. It used a phosphorescent dye that changed a delay flash (ie you blinked a light, the dye would absorbed and blink back after a delay) based on temp and o2.CO2 was measured with infrared but water also absorbed it, so you need to heat things up enough to not have water. It can be small, but not watch small.
All and all interesting stuff!
by roland35
7/4/2026 at 1:50:48 PM
> CO2 was measured with infrared but water also absorbed it, so you need to heat things up enough to not have water. It can be small, but not watch small.Can't you just measure CO2 "naively"; but then also, separately, measure rH; and then use the rH value to grab a research-calibrated LUT to pass the raw CO2 value through?
(I presume this is why all the little standalone CO2-sensor boxes you can buy also have rH displays. They're measuring it anyway to normalize the CO2 value, so they may as well make it a feature and display it.)
by derefr
7/5/2026 at 12:09:22 AM
You could maybe, but water tended to collect on the surface (this was exhaled breath, so pretty humid).Maybe if it was ambient air and not breath the humidity might not be as bad?
by roland35
7/4/2026 at 10:00:57 AM
Electrochemical pile style oxygen sensors continuously deplete themselves whether actively measured or not. Common smart home oxygen piles have a fixed lifetime of a few years, and they're quite sizable (probably about as much volume as a whole smartwatch). Putting the same chemistry in an even smaller package would likely result in lifetime measured in hoursby picture
7/4/2026 at 12:34:53 PM
I assume this is because of diffusion of materials at elevated temperature. The sensor would, I think, require a lower temperature than an electrolyzer, since the current would be much lower. But it would be best if lower temperature solid oxide electrolytes could be discovered.by pfdietz
7/4/2026 at 10:20:08 AM
The ones in cars need to be heated up quite a bit in order to work, and you still need reference air. Otherwise, I'm pretty sure that CO2 isn't a problem but rather an indication of a lack of oxygen in the first place, so it technically could work... just not if you're measuring the environment itself.by Lwerewolf
7/4/2026 at 10:54:07 AM
This is in theory not a problem: getting an oxygen sensor to 700 degrees if it's a tiny spec on a chip is not necessarily hard or would even require a lot of power.But...oxygen concentration is essentially indepedent of CO2. We measure CO2 at part per million levels, whereas O2 is 20% of the air.
(In that context CO2 is surprisingly toxic given that 1000 ppm can impair mental acuity).
by XorNot
7/4/2026 at 4:05:17 PM
> whereas O2 is 20% of the air.The goal of a gasoline engine's sensor is to accurately and precisely measure the point where O2 concentration reaches zero, so ambient air levels are not quite as relevant.
by coryrc
7/4/2026 at 11:26:42 AM
No, it's nonsense to assert that CO2 is due to a lack of oxygen.by OutOfHere
7/4/2026 at 10:00:28 AM
I don’t think we actually care about co2 levels. I think we use them as a proxy for o2 levels (same as our bodies do). So your idea would be great.by noja
7/4/2026 at 10:57:53 AM
> I think we use them as a proxy for o2 levels (same as our bodies do).Probably. ISTR that depriving a body of oxygen results in a different response than overloading the body on CO2. It's why if you completely displace all air in the room with CO2, people choke, panic, etc, but if you use Nitrogen, people just keel over dead without realising it.
by lelanthran
7/4/2026 at 11:48:03 AM
The evolved response to CO2 is part of the human body’s ability to filter and remove CO2 via the respiratory system. AFAIK we don’t have similar capacity for Nitrogen because it’s not a primary waste product of that system.by mathgeek
7/4/2026 at 12:23:56 PM
Dissolving CO2 in water creates some carbonic acid (H2CO3) that will decompose back to water and CO2 when the CO2 concentration drops. Blood has a fair bit of water, and carbonic acid is much easier to detect than oxygen or nitrogen gasWe evolved to detect CO2 because that's by far the easiest thing to detect that's still a reasonable proxy for the performance of our respiratory system
by wongarsu
7/5/2026 at 2:19:35 AM
We evolved to detect CO2 because it was an evolutionary advantage over those who didn’t.by mathgeek
7/4/2026 at 10:57:05 AM
This is extremely wrong: CO2 impairment kicks in around 1000 ppm[1] possibly lower.You can hit this breathing by yourself in an unventilated 3x3m room (literally measured in my house).
by XorNot
7/4/2026 at 11:10:19 AM
You hit it even easier when driving in a car with the internal circulation turned on to keep nasty fumes out.by spockz
7/4/2026 at 11:26:03 AM
In a car with Recirculation Mode on Levels routinely spike between 1,500 and 4,000 ppm within 20 to 30 minutes.I wonder how many driving accidents can be saved by having a co2 monitor in the car.
by uxhacker
7/5/2026 at 12:32:49 AM
I had to drive a rental car for a bit recently, after getting rear-ended, and I was shocked to discover that it defaulted to recirculation mode every time it was turned on, regardless of whether you'd turned it off the previous time. I felt light-headed in it a few times before I realized I needed to manually turn recirculation off every time. Horrible behavior, and I don't doubt that it's responsible for many accidents.by eurleif
7/5/2026 at 12:17:45 AM
there is some ambiguity here. submariners are exposed to really high co2 levels and are doing fine. it's possible that regular high co2 is just a proxy for bad air, and that you can acclimate to purely high co2 pretty well.i have felt bad in high co2 environments before but i have never been in a controlled high co2 environment.
by teravor
7/5/2026 at 12:38:50 AM
I'm not implying permanent effects. The studies involved show a marginal reduction in cognitive reasoning on standardized tests.Which is the point: if you're in a room trying to do deep work, that's likely a problem. I suspect submarines are all over the place here: you might be exposed to higher levels routinely but you also have regular access to chemical scrubbers and decent ventilation. I'd be fascinated to know what levels are tracked as normal.
by XorNot
7/5/2026 at 12:58:47 AM
apparently those scrubbers are less efficient the lower the co2 is (also need to move much more air which ruins stealth). iirc submarines are routinely exposed to multiple thousands.by teravor
7/5/2026 at 2:51:00 AM
It does look like this has been studied: https://pubmed.ncbi.nlm.nih.gov/29789085/ and found no significant effects.So quite possibly an adaptive response?
by XorNot
7/4/2026 at 10:59:48 AM
I'm pretty sure that in a room where we replaced nitrogen with co2, we would be dead even if O2 concentrations were the same. Something about partial pressure. I notice AI explanations agree with me (not going to copy and paste them).by vintermann
7/4/2026 at 11:50:03 AM
EDIT: ignore this; I was confused / misinformedIt's about pH. CO2 creates carbonic acid when it dissolves in water. Your blood pH, in turn, controls how much you feel like you need to breathe. So with high CO2, your respiration rate slows down, and that can lead to low oxygen levels.
Note that the physiology and biochemistry of this is complicated (e.g. blood is a very good pH buffer and it's actively regulated by kidneys etc) and it's very much a nascent field of research, so I think AI will be overconfident and hallucination-prone.
Source: I worked in high-co2 caves for my PhD so have read about this a lot. I always carried a CO2 monitor. Our rule was to get out if we saw 20,000 ppm or greater. I spent thousands of hours above 10,000ppm.
by foobarbecue
7/4/2026 at 1:05:57 PM
My medical student flatmates were talking a lot about acidosis and alcalosis :)It was the first time that I heard about them. These basically never happen if your body and environment are halfway decent, but they are important in exceptional situations.
by ahartmetz
7/4/2026 at 12:09:26 PM
Wouldn't high CO2 make you breath faster?by dummydummy1234
7/4/2026 at 12:20:58 PM
Interesting, the linked article does say that.Pretty sure I learned the effect was the opposite (high CO2 --> slower respiration). Note that that was ~15 years ago when I would have read that. Maybe I just misunderstood, or thinking has changed.
edit: reading now I see I was wrong about this. Thanks for the correction!
by foobarbecue
7/4/2026 at 12:38:32 PM
You are right about the pH implications, but respiratory acidosis leads to hyperventilation, not hypoventilation. CO2 will kill you regardless of oxygen supply.by jijijijij
7/4/2026 at 10:52:53 AM
What makes you think that?by dgellow
7/4/2026 at 10:03:47 AM
We do.by noosphr
7/4/2026 at 11:28:42 AM
Huh. You don't know that, and are making it up. It's almost certainly false.by OutOfHere
7/4/2026 at 1:06:07 PM
Sensiron STCC4 uses thermal conductivity sensing thats very compact (4x4x1.2mm). It's pretty new to the market, but maybe in the future it'll happen.by NathanielK
7/4/2026 at 10:27:09 AM
Mesh with the other Apple/et al devices in the room to take multiple samples and aggregate the results for an overall picture of the ambient co2by kingkawn
7/4/2026 at 10:58:02 AM
Just waiting for the followup post on HN: How I sent CO2 warnings to my entire office using an ESP32by stonegray
7/4/2026 at 10:37:44 AM
What if a movie theater puts an Apple CO2 meter next to an air inlet? Everybody will think the air is safe.by amelius
7/4/2026 at 11:38:00 AM
If that’s the sole source and the application does thoughtful analysis it could determine that there are sections of the room that are better than others, yesby kingkawn
7/4/2026 at 12:54:27 PM
But realistically, using what sensors?And (maybe less realistically) what if the theater puts 5 Apple sensors inside a sealed CO2-free chamber, spread around the room?
by amelius
7/4/2026 at 12:56:35 PM
That’s the point of this thread that each device would have a small sensor that would sync and aggregate with others in the roomby kingkawn
7/4/2026 at 12:58:26 PM
I think the thread established that CO2 sensors are too bulky for that.by amelius
7/4/2026 at 3:54:08 PM
So were most other sensors before Apple (and their suppliers) miniaturised the sensors. Gps and imu was huge in the 90s, several pound each.by mrgyro
7/4/2026 at 11:30:59 PM
But this is wishful thinking.by amelius
7/4/2026 at 7:48:46 AM
I guess the problem is with the price of the sensors. Just look how expensive the Aranet 4 home shown in article is. There are worse devices for less like the IKEA alpstuga. I also don’t know how much electricity they pull.by legulere
7/4/2026 at 8:05:44 AM
I would hesitate to say the IKEA is worse. Inside the IKEA is a reputable Sensirion all in one sensor module. It's much cheaper and smaller because the CO2 sensor in it is using different (newer) technology that only released a few years ago from Sensirion.(Upd: the IKEA does have lower accuracy, with ±100 ppm instead of ±30 ppm. From the SEN63C datasheet)
by Liftyee
7/4/2026 at 9:30:12 AM
Worse specs? Sure. Worse value? I don't think so. Worse accuracy? Perhaps not either.A price of 30 EUR makes this sensor really easy to pick up. For the same price as one Aranet (~180 EUR) the typical household can place a sensor in every room of the house. Which provides far more accurate readings for the whole house than just one high-end sensor in one room.
by yoshuaw
7/4/2026 at 2:16:59 PM
I have one IKEA Apstuga on my desk, sitting right next to a good CO2 monitor. Since Apstuga uses worse approach (heat) rather than light as the good sensors, it diviates around +/- 100 ppm. For example the correct CO2 is 610 ppm and IKEA's sensor shows 552 ppm with is reasonably close. So the trend will be correct and the values will not be.But when it goes over the safe limit it should be enough to decide to ventilate.
by freefaler
7/4/2026 at 9:11:26 AM
No, it is crap. Yes, it is Sensirion, but it uses a thermal conductivity sensor, which is a very indirect method of measuring CO2. One part of the sensor emits heat and the other senses it and the idea is that heat transfer changes with different CO2 concentrations. However, a lot of other factors influence this as well, such as ambient temperature/humidity (which is why the sensor incorporates measurements from an SHT sensor), but also gas mixture, etc. You only get good readings at lab conditions. Even below 1000 ppm, I would often see readings that are 300 ppm from more expensive, known-good CO2 meters.If you want a CO2 meter on the cheap, either wire up an optical NDIR sensor like the SenseAir S88 (22 Euro) up to an esp32, which is possibly the best sensor you can get for the money (slightly cheaper version of the sensor that the AraNet4 uses). Or if you want something standalone with a display, get the SwitchBot Meter Pro CO2 for ~50 Euro, which uses a photoacoustic NDIR, but is still miles better than the sensor in the ALPSTUGA. Can also be hooked up with HA through an ESPHome BLE proxy or with the SwitchBot Hub.
You can find a comparison of the IKEA sensor with other affordable sensors here:
https://danieldk.eu/hardware/smart-home/ikea-alpstuga
(Upd: the IKEA does have lower accuracy, with ±100 ppm instead of ±30 ppm. From the SEN63C datasheet)
You forget to mention that it is ±100ppm plus ±10% of the ambient ppm, which makes a big difference. At 1000ppm it's ±(100ppm + 0.10*1000) = 200ppm and that's only in an environment with 25C, 50% RH, and 1013 mbar. So, that does not tell you much, given that thermal conductivity is very sensitive to environmental factors.
by microtonal
7/4/2026 at 9:19:30 AM
if you just want to know if CO2 is too much, 300ppm precision is fine.I dont need to know the exact level, just give me a green/yellow/red LED and make it cheap so I can have a sensor in every room
by nok22kon
7/4/2026 at 9:20:51 AM
No, it's not. You generally want to ventilate an office when you reach 1000ppm, but then the IKEA will often warn you already at 700ppm. 700ppm is fine.by microtonal
7/4/2026 at 10:04:46 AM
"Generally" is a vibe measurement to begin with. You won't notice any difference at all between 700ppm and 1000ppm. It's once you start hitting 2000ppm you are getting noticeable brain fog.by Gigachad
7/4/2026 at 1:11:36 PM
Had bad ventilation in my old apartment (built 1888) so got a co2 monitor. Started feeling the effect at 1100-1300ppm, so would open it in home assistant and check, never below and never above really. During winter when it was -10 so couldn't keep the window open all the time.by Hikikomori
7/4/2026 at 11:36:34 AM
I disagree. I feel a very steady and progressive deterioration starting at 600 ppm. It becomes significant at 800 ppm. The studies back up the latter threshold.by OutOfHere
7/4/2026 at 12:37:31 PM
Unfortunately it will be hard for you to know how much of that effect is placebo. Unless you tested this with some kind of double-blind setup.by teiferer
7/4/2026 at 2:55:41 PM
You're not wrong, but indoor CO2 at these sub-1000 levels is a useful proxy metric for bioeffluent VOCs which are an objectively tiring subset of total VOCs. Ventilation lowers both. This explains the observation better than nocebo theory. See https://www.aivc.org/resource/effects-carbon-dioxide-and-wit...by OutOfHere
7/4/2026 at 1:39:20 PM
You would not notice a difference if you weren’t checking the CO2 ppm. You primed your brain to ‘feel’ the effects of higher CO2 by reading a study and are experiencing the nocebo effect.If it makes you feel better I don’t see a problem with it.
by quickthrowman
7/4/2026 at 2:50:31 PM
Indoor CO2 is likely overrated here at these sub-1000 levels but it's a useful proxy metric for bioeffluent VOCs which are a tiring subset of total VOCs. Ventilation lowers both. This explains the observation better than nocebo theory. See https://www.aivc.org/resource/effects-carbon-dioxide-and-wit...by OutOfHere
7/5/2026 at 3:29:15 PM
Interesting study, thanks for sharing! I am starting to see more space temp/CO2 combo sensors in commercial office conference spaces, if the CO2 rises above the setpoint, the VAV opens to let air in to reduce CO2 (and bioeffluent VOCs, according to this study.)by quickthrowman
7/4/2026 at 9:37:57 AM
you assume that the error will always be in one directionand if sometimes you ventilate a bit sooner than required, at 700, what?
businesses will not put $200 meters in every room
by nok22kon
7/4/2026 at 12:29:49 PM
Have you looked at the prices of meeting room furniture? A $200 meter is not a significant cost measured against what it costs to furnish the room in the first place. It only becomes significant is you treat it as a line item disconnected from the room it's inby wongarsu
7/4/2026 at 11:33:58 AM
businesses will not put $200 meters in every roomThere are good $50 Euro meters. Besides that, I am not sure if that is true, at my wife's workplace, they put high-end CO2 meters in every larger room where multiple people meet. Admittedly, this was during COVID, so a lot of organizations were using CO2 levels as a proxy for finding whether a room was properly ventilated.
by microtonal
7/4/2026 at 11:13:52 AM
Presumably there is still the need to ventilate. So the concentration can also be measured more centrally. That is how the mechanical ventilation unit in my house works. For both humidity and CO2.by spockz
7/4/2026 at 12:28:41 PM
$200 is nothing compared to the lost productivity.by sscaryterry
7/4/2026 at 11:37:15 AM
You put one CO2 sensor in the return air duct and tie it to outside air control.by doobiedowner
7/4/2026 at 12:16:27 PM
You generally want to ventilate almost continuously, so if a circulation fan kicks on at 700 instead of 1000 that's really not a big deal.by andrew_lettuce
7/4/2026 at 11:48:41 AM
But if I open a window at 700ppm, so what?by Scroll_Swe
7/4/2026 at 5:21:55 PM
Maybe you live in a place where the room temperature is the same as outside. Here in winter, it means sitting in the cold.by microtonal
7/4/2026 at 8:15:36 PM
No I live in Sweden.You can open the window for a bit to air out, should be done even in the winter :)
by Scroll_Swe
7/4/2026 at 12:02:05 PM
Suddenly there's not enough CO2 in the room and you get overly awake! Bummer! /sby cassianoleal
7/4/2026 at 7:52:00 AM
I got the ikea sensor, I’d say it’s way more accurate than you need for personal use. I wouldn’t use it as a scientific instrument but it’s well good enough to see if the room is ventilated enough.I was shocked to see just how fast CO2 climbs while in a room, and how just opening the window just a crack was enough to restore the room to baseline co2.
The thing runs on usb 5v so the power consumption is negligible. It also plugs in to home assistant great.
by Gigachad
7/4/2026 at 9:16:20 AM
I have HA send me a notification to ventilate my office when the air reaches 1000ppm CO2. The IKEA ALPSTUGA is often off by 300ppm even under 1000ppm. If I'd use it, I'd be getting notifications at 700ppm.It is a thermal conductivity sensor, which is a very indirect way of measuring CO2 and is very sensitive to environment factors. You only get somewhat good readings in lab conditions.
Don't by the ALPSTUGA for anything but very rough trends, there are much better affordable options.
by microtonal
7/4/2026 at 9:23:11 AM
Within 300 ppm is more than good enough. Realistically 1000 ppm is not that bad. The average meeting room is multiples of that.Also in my experience it’s much more accurate than that.
by Gigachad
7/4/2026 at 9:26:36 AM
I notice that thinking becomes less clear when going above 1000ppm, so I let HA send a notification at 1000ppm. With ALPSTUGA it would send already at 700ppm. By the way, above 1000 the divergences become even larger due to the inaccuracy also being 10% of the ambient CO2 concentration (in optimal circumstances, probably larger IRL). So, suppose you want to be notified at 2000 ppm, the IKEA sensor might already do so at 1500 or 1600 ppm and it continuously drifts, so it's not like you can use a particular offset.Besides that, what's the point? There are much better meters in a similar price class. As an additional benefit, they can last months or up to a year on two AA batteries.
ALPSTUGA is an inferior product.
by microtonal
7/4/2026 at 10:08:18 AM
Can you recommend some?by summm
7/4/2026 at 11:42:31 AM
Mentioned two here: https://news.ycombinator.com/item?id=48783879by microtonal
7/4/2026 at 10:14:09 AM
>With ALPSTUGA it would send already at 700ppm."oh no I am getting too much fresh air"
I get your point but come on.
by Scroll_Swe
7/4/2026 at 5:19:50 PM
In some situations it means opening a windows, with big temperature drops when it is cold outside.At any rate, this is really a weird discussion, because you can get far more accurate meters at similar price points. Why waste your money on a much worse meter?
by microtonal
7/4/2026 at 8:16:07 PM
The IKEA one looks cuter :3by Scroll_Swe
7/4/2026 at 8:38:15 AM
Can it work with Zigbee network or is Matter/Thread required?by odiroot
7/4/2026 at 8:48:22 AM
I'm using a bunch of IKEA's "smart home" stuff, all via Zigbee+HA, works great. Look for the Zigbee icon on the package, and the pairing for Zigbee vs their own home controller might have slightly different pairing sequence on the device, otherwise it just seems to work.by embedding-shape
7/4/2026 at 9:18:55 AM
ALSTUGA does not work with Zigbee.They recently overhauled their lineup and replaced all Zigbee devices by Thread + Matter. Some of the new devices (mostly those who support TouchLink, e.g. some of the lights) have a secret pairing mode with which you can use them with Zigbee, but it's only a subset of the new products.
by microtonal
7/4/2026 at 9:42:03 AM
> They recently overhauled their lineup and replaced all Zigbee devices by Thread + Matter.Uuh, seems not keeping up with social media finally backfired. That sounds horrible! So far IKEA been a great experience when it comes to HA+Zigbee stuff, and I started buying stuff relying on they'd keep just keeping up with that, really sad to hear they've changed course.
The "secret pairing mode" stuff sounds the same as currently/before though, but they only do so for a subset is new and hope they again change their mind.
by embedding-shape
7/4/2026 at 10:01:36 AM
Thread is significantly better. Zigbee relied on proprietary hubs and apps or hacky work arounds. Matter over thread devices don't need a brand specific hub or app. You can literally control the new ikea products direct from a modern iphone which includes a thread radio, no hub, server or app required.If you already own the ikea hub, they secretly put thread radio in it which was just sitting unused in preparation for this range.
by Gigachad
7/4/2026 at 10:20:57 AM
It's complicated. Matter over Thread is indeed nice in that it you only need generic Thread and Matter servers. It also makes it easier to share credentials between ecosystems. Thread itself is also a pretty nice standard technically.There are also strong downsides though, one is privacy and future cloud lock-in. Zigbee is fully local. Previous Thread standards added the option for NAT64 so that Thread devices can access the internet and there were some Thread + Matter devices that already require internet access for full functionality (IIRC some Nuki smart locks, but I might misremember). However, Thread 1.4 also adds support for Thread devices to get a globally routable IPv6 address. The Thread 1.4 whitepaper is pretty blunt about what this enables:
Simplified Cloud Integration: Thread devices can now seamlessly connect directly to cloud services, enabling remote control, monitoring, and over-the-air firmware updates.
https://www.threadgroup.org/Portals/0/Documents/Thread_1.4_F...
The fact that Thread and Matter are strongly pushed by Google, Apple, etc. should tell you enough.
Now, a TBR may simply allow you to disable NAT64 or globally routable IPv6 addresses (e.g. Home Assistant's addons), but many consumer implementations don't. E.g. the Apple TV is a Thread Border Router and does not allow disabling NAT64, so Thread devices can access the internet, send analytics, and can be cloud-controlled.
Also, the ecosystem is still pretty immature, as a result of which you can encounter issues, typically resulting in unstable device connectivity. E.g. TREL does often does not work well. Apple has some hacks to fix most of the issues, but it only works well between Apple devices. So it's generally the best to avoid combining multiple TBRs into the same network.
by microtonal
7/5/2026 at 2:28:02 PM
Thanks for this info. I've been patiently waiting for Thread/Matter devices so that I could just use my AppleTV as the TBR and not need any Zigbee gateway. And not need HomeKit-specific devices; just use generic ones.But I'm certainly not about to let simple IoT devices have any internet access at all. Being unable to block this on the TBR as you suggested would be mandatory for me, and not possible on AppleTV.
by jonpurdy
7/4/2026 at 10:59:56 AM
> Thread is significantly better.Better than what already exists and is deployed? I dunnno, hardware already in use always beat "hardware conceptually better but I don't have it", that's why Zigbee is better, for me. Protocols much like everything in the world, isn't correct/incorrect or universally "better", it's all down to use cases.
Personally, as someone who started to rely on IKEA providing Zigbee devices, Thread is obviously worse, because 100% of the devices I have are already Zigbee and not Thread.
by embedding-shape
7/4/2026 at 11:06:48 AM
Ikea preemptively sorted this out by putting thread radio in their hubs years before rolling this out. There's also thread radios in the latest chromecast, apple tv, and loads of other products. If you have a single thread border router in your house from any brand you'll be able to connect to any thread device from any brand. Phones can also directly control thread devices without needing any network or hub.It's a vastly better system and the transition period is so smooth because the smart home companies have been deploying the thread hardware for years before anyone started using it.
by Gigachad
7/4/2026 at 11:40:23 AM
smart home companies have been deploying the thread hardware for years before anyone started using itAlso worth mentioning that many modern Zigbee radios can also be Thread thread radios using different firmware. There are even multi-PAN radios that can do Zigbee and Thread at the same time. Some smarthome hubs use multi-PAN (e.g. Homey Pro), but it's generally recommended against now because of lower reliability.
The same applies to devices, e.g. some of the new IKEA devices work over Thread or Zigbee (Zigbee pairing is triggered using a non-documented sequence, presumably they added support for TouchLink). Or e.g. the Aqara FP300, which can be flashed with Thread + Matter or Zigbee firmware. It works because the same radio can be used for both protocols.
by microtonal
7/4/2026 at 1:13:36 PM
This wasn't true for zigbee either. I used a zigbee usb stick with home assistant, could use any stick that was supported.by Hikikomori
7/4/2026 at 10:00:17 AM
Yeah, I bought a bunch of INSPELNING smart plugs when they were clearing out the inventory. The new GRILLPLATS switches are more compact though, which is nice.by microtonal
7/4/2026 at 8:59:00 AM
It’s part of the new range which is all matter over thread only. The existing ikea hub can do thread though.by Gigachad
7/4/2026 at 8:21:49 AM
> The thing runs on usb 5v so the power consumption is negligible.There’s a huge leap from that to the power consumption being low enough to be integrated into a smartphone, as demanded by OP.
by p-e-w
7/4/2026 at 8:44:49 AM
I don't think power use is the issue. I have this cheap CO2 sensor: https://www.domadoo.fr/en/devices/5882-heiman-zigbee-air-qua... which draws 0.5W. This includes thermometer and humidity sensor, Zigbee transmission, and acting as a Zigbee router, but it gives us an upper bound. It also measures continuously (picks up someone breathing on it within 10s), which is overkill. A phone could measure CO2 levels once every 10 minutes which would average under 0.01W, so that would work.However, this assumes the sensor would fit in a smartphone, which is not a given. And these things need air flow. And they also wouldn't work while the phone is in a bag or a pocket.
by progval
7/4/2026 at 9:34:59 AM
>A phone could measure CO2 levels once every 10 minutes which would average under 0.01W, so that would work.Not sure about that, at least NDIR sensors have to be at certain elevated temperature to work and they do some preheating when you turn them on from standby.
So it's not possible to just measure less often as then energy would have to be spent on heating the sensor.
by nnevod
7/4/2026 at 8:53:26 PM
I've got a NDIR CO2 sensor about 6 weeks into a supposed 1 year battery life, still reporting 100% battery. Power use is very low since it only fires up the CO2 sensor every 30 mins.by ac29
7/4/2026 at 10:30:26 AM
Ruuvi Air[1] seems to be close to the middle in both price and CO2 measurement accuracy between aranet4 and the IKEA device. I don't have personal experience with Ruuvi Air specifically, but have been using their cheaper Ruuvi Tags (that don't measure CO2) for temperature, humidity and air pressure measurement at home and office.by mdf
7/4/2026 at 8:33:23 AM
> I also don’t know how much electricity they pull.It can't be much, since the Aranet 4 can run for years on 2 AA batteries.
by SideburnsOfDoom
7/4/2026 at 12:45:38 PM
Is it a tually lower oxygen in the blood that's the problem, or higher co2? I'm not sure if having high co2 automatically implies lower oxygen, I have no idea at all but feels like it may not necessarily be strictly. Linked. Also, are the cognitive issues of low oxygen the same as high co2 or do they produce different effects?by alienbaby
7/4/2026 at 12:48:45 PM
From what I learned from Apollo 13, even with O2 in the air, CO2 can still be poisonous.by fhdkweig
7/4/2026 at 6:09:22 PM
I always come at this angle.If you had the data, what would you do to change it? Would you recommend everyone go outside? You can do that without the data.
Would you wear your own oxygenated supply of air? You can do that without the data.
Would you make recommendations that the office should improve air quality? You can do that without personalized real-time data.
I'm not against data in general, but the idea that if only we had data we would make changes in our lifestyle is not valid. We see it all around us.
We had bathroom scales for over a century, but the data or insights didn't put a dent in the obesity epidemic.
You're right about "the problem will solve itself", but it isn't the data that will help to solve the problem, it's creating a simple and obvious solution.
A friend has a start-up in the commercial air quality space which solves for this problem (in some ways). But the benefit isn't the air quality, it's the cost of maintaining the healthy levels required in commercial buildings. Air quality is the secondary benefit of reduced electricity demand in air circulation.
by pedalpete
7/4/2026 at 2:33:53 PM
I built a conference badge with a proper, laser-based CO2 sensor.It didn't work very well because just by virtue of being near me all the time, it didn't get a very good measure of the average room contents.
by misnome
7/4/2026 at 11:55:28 AM
There is one in the EcoBee Premium and we use it to automatically drive our HRV (heat recovery ventilation.).It is better to have it in the HVAC system than in your phone anyhow:
by bhouston
7/4/2026 at 8:45:58 AM
> Raising awareness is the only real solution.You'd have to raise awareness on every single person in the room and them sustain pressure to the organization in order to have proper CO2 levels in the room/organization.
And then you have to align every other person on every other organization to do this as well and hope for the best.
Or, you can do the right thing and have the state introduce regulations
by stein1946
7/4/2026 at 10:25:50 AM
I don’t think that’s right. If people have an easy way to measure the levels, and they can see something on their phone like ‘you spent 8 hours today above 2000ppm CO2’ then the room will care a lot more than it did before, and people will be able to quickly see whether they have improved things. At my employer, I think it took us around 1000 employees until we randomly hired someone who happened to care a lot about CO2 levels and I think they managed to cause a decent increase in the amount that the company cared / thought about levels (this was around the end of Covid though so part of this may have been due to using CO2 levels as an indication of insufficient ventilation/air filtration).by dan-robertson
7/4/2026 at 11:18:31 AM
Depending on the state, newer buildings do have regulations on air ventilation and quality.The rooms being discussed here are mostly ones which would have been built before this was taken more seriously. Classrooms, older office buildings, etc.
NYC is full of buildings which would never pass any code today but are still happily occupied. It’s a trade off, I think.
by joenot443
7/5/2026 at 8:26:14 AM
It doesn't work like that. I've been made aware thanks to this post, and tomorrow I'll be placing CO2 sensors in every meeting room in the company I work at, and mandating an open-windows or air-circulating policy above 800ppm.You don't need to make everybody aware, you just need to make the right people aware.
As for the State... Mine mandates that nobody can use the laptop's keyboard, they must use an external keyboard so the laptops' screens can be risen to eye level.
We have the external keyboards and the risers, and nobody uses them.
The State usually finds the worst and most wasteful solution available. Only fools trust the State to solve their problems.
by Ikatza
7/4/2026 at 10:16:27 AM
Can't you just open a window a bit?by Scroll_Swe
7/4/2026 at 10:34:09 AM
In lots of modern office buildings you can’t.by hosteur
7/4/2026 at 12:20:48 PM
ah, sadly that was in my last modern one. Thankfully we can open the windows in this one :)Best solution.
by Scroll_Swe
7/4/2026 at 9:03:41 AM
I can just imagine the horrors and skin crawls that your last sentence has evoked in some people's minds. Not the state!!But seriously, so much care needs to be taken here. OK, well "care" at least. Employers certainly would benefit from scrubbing CO2 from the air, in terms of productivity. I'm willing to bet that with central air it would be quite easy, and even with heat and AC off, lots of places still circulate the air regardless.
So the central place to scrub is already there.
But then you have other issues. Such as, will your body adapt to 8 hrs of reduced CO2, and then you become torpid and barely awake when not at work. Such a horrid thought, that is to me. And what if employers learn that the tiniest boost of O2 helps too! Now your body becomes accustomed to that, and what are the long term effects there?
I can personally envision myself being concerned. I guess the legislation could be crafted to "the same CO2 levels found just outside of downtown city core" or some such blather. Maybe even same for O2. So that you're at least pegged to something normal for the area.
Maybe that's where the state could come into play. A simple, highly accurate monitoring station which has an API to be polled.
Come to think of it, CO2 and O2 rates fluctuate during the 24 hour cycle. Trees need O2 to live, but only produce O2 during the day. And so differing amounts of light might mean up and downs in these numbers. It may be another circadian rhythm. Getting it the same as in a nearby forest, might be the healthiest thing of all.
by b112
7/4/2026 at 9:48:37 AM
In practice, one would use energy recovery ventilation to exchange air with outside rather than a CO2 scrubber (not clear if you actually meant a scrubber).The place to look is existing codes for ventilation. Exempli gratia: https://dos.ny.gov/system/files/documents/2020/09/2020-mcnys... (see PDF page 46). Regulations to enforce outside air being brought into human spaces already exist.
I have been in some office buildings in United States which had CO2 monitors in each meeting room, and the ventilation would engage to control CO2 below a set level. We would entertain ourselves by exhausting our lungs onto the sensors to trigger the ventilation system.
by i_am_proteus
7/4/2026 at 12:17:07 PM
I should have said it more clearly, I just thought HN would take this stance regardless. If you tell an employer to ensure CO2 levels, and it shows an improvement in productivity, employers may think "Hmm. Let's improve this further!" and add O2 as well.In terms of outside air, a lot of US cities I think would not benefit from that, all that much. Especially during certain parts of the day, with a lot of smog.
But regardless, all that entered my mind was "Once employers are required to add any form of scrubbing, and perhaps O2 injection, they'll over do it for optimal employee output." Regardless of whether it's helpful once the employee leaves the workplace.
I'm not against this, I'm just actually saying the regulation should be locally defined.
by b112
7/4/2026 at 9:17:50 AM
You’re talking about oxygen like it’s California Rocket Fuel or meth.by floam
7/4/2026 at 5:47:05 PM
Welcome to HN. Eternal September has arrived here at last.by MajorTakeaway
7/4/2026 at 3:02:56 PM
Controlling indoor CO2 is important, but it's a proxy metric for the escalation in indoor bioeffluent VOCs which are a tiring subset of total VOCs. This is why scrubbing indoor CO2 will by itself never produce the pro-cognitive result you want. See https://www.aivc.org/resource/effects-carbon-dioxide-and-wit...Scrubbing indoor CO2 is sensible only when you want to go below the outdoor CO2 level, not at levels above it.
by OutOfHere
7/4/2026 at 9:13:35 AM
It is not that complicated. You need to introduce CO₂ threshold levels that make sense from a medical standpoint. Then you need to enforce them in the same way other basic environmental regulations or worker rights are enforced in regions of the world where these work.The main question is: If your workplace, city, whatever forces you to work or live in an harmful/unhealthy environment, do you have any realistic course of action to improve the situation? In the US you would call this (gasp) regulation, I would call it a basic human right.
If we talk about stairways, nobody complains about building regulations that mandate handrails. CO₂ levels are not totally different.
by atoav
7/4/2026 at 7:14:47 PM
This sounds like a solution in search of a problem. If you feel dizzy at random moments, see a doctor soon.by 0ckpuppet
7/4/2026 at 9:02:07 AM
I was looking at CO2 sensor module boards this week and the sensors themselves are quite large and the floor price is $15ish.by zeafoamrun
7/4/2026 at 10:09:26 AM
Those $15 ones are also straight up scams. They just estimate (lie) for the readings based on other sensors.by Gigachad
7/4/2026 at 9:09:51 AM
And I believe the accuracy is also not great on these cheap ones. The product in the OP's photo costs $200 where I live! And ISTR finding the sensor itself contributes a lot to this cost.IIUC they also need fans. The one I have in my home has one that's actually integrated into the sensor unit.
by bjackman
7/4/2026 at 12:54:33 PM
This would probably be the biggest awareness thing tech could do for climate change as well.by jeffybefffy519
7/4/2026 at 1:14:40 PM
[flagged]by 256dpi
7/4/2026 at 8:16:47 AM
[dead]by aaron695
7/4/2026 at 6:24:44 PM
[dead]by fatata123
7/4/2026 at 9:56:21 AM
CO2 and all other air quality indexers have to be very carefully calibrated regularly. It's not some slop you can just throw into a consoomer cheap iot device.Article author completely ignores this for the obvious reasons.
by reddozen
7/4/2026 at 10:08:40 AM
For the purposes of indoor ventilation monitoring you can calibrate by occasionally exposing the sensor to fresh air. Either taking it outside or just the room not having people in it. The sensor will treat the lowest reading it gets as 400ppm since this is what outdoor air is.A sensor mounted in the office will get calibrated every night when the office is empty.
by Gigachad
7/4/2026 at 11:39:47 AM
The outdoor CO2 is rising every year. It is not fixed at 400 ppm. The calibrations you speak of are fake. A good sensor can be expected to remain within 10% of reference for ten years.by OutOfHere
7/4/2026 at 2:50:14 PM
The outdoor CO2 is rising every year. It is not fixed at 400 ppm.But close enough for most purposes. We aren’t doing laboratory measurements here, I just want to know whether or not to open a window.
by mikestew
7/4/2026 at 2:53:51 PM
You don't need to routinely calibrate a good device at all for that purpose. It already will maintain a reading within 10% of the real value. If it's not doing that, it's a bad device. It's very possible your calibration process will actually miscalibrate it and increase the error. Already the outdoor CO2 level is 430, not 400, so you'd be introducing at least a 7% error by calibrating it to 400.What I do at home is I have multiple meters bought over the years, not all at once. If one of them is too deviated, I can replace it, but this deviation has never happened in the last five years. It did happen once about ten years ago with an old model.
by OutOfHere
7/5/2026 at 1:44:51 AM
If you want to make measuring CO2 your obsessive compulsion then sure, buy a lab grade instrument. If you want to get a practical reading of the air quality that is more than good enough, affordable, and looks nice on your bedside, the ikea one is a great option.by Gigachad
7/4/2026 at 11:41:05 AM
Not really. For ventilation purposes, a good sensor remain within 10% variation for nearly ten years. We are not running a controlled science experiment here.by OutOfHere
7/4/2026 at 7:33:20 AM
Apple watches already have a blood-oxygen sensor so it's covered, albeit indirectly.by scoot
7/4/2026 at 7:48:48 AM
I don't think that's true at all. Capnography, the measure of carbon dioxide partial pressure is wholly separate from pulseox:> Pulse oximeters have some limitations. They can only employ light at two wavelengths. Thus the devices can only distinguish between hemoglobin and oxygenated hemoglobin. When carboxyhemoglobin and methemoglobin are also present, there are two additional wavelengths required for differentiation. In the presence of elevated carboxyhemoglobin levels, pulse oximetry overestimates the true saturation of oxygen as carboxyhemoglobin binds with a higher affinity than oxygen. In the case of carbon monoxide poisoning, the absorbance spectrum of carbon monoxide is very similar to hemoglobin, which results in a falsely high level of oxygen (overestimation of oxygen saturation) ...
by oasisbob
7/4/2026 at 9:50:50 AM
>Pulse oximeters have some limitations. They can only employ light at two wavelengthsWhy only 2?
by benj111
7/4/2026 at 6:32:53 PM
I think that might be a descriptive statement based on what's in the market, vs hypothetical implementations.by oasisbob
7/4/2026 at 7:58:19 AM
I don't think that's safe to assume at all, for two reasons:1. CO2 has effects on the human body of its own that aren't simply a lack of oxygen, and vice-versa. [0]
2. The baseline proportions involved aren't close, so even doubling CO2 isn't going to show up easily as a large swing in in oxygen%.
For example, the article references a study where the CO2 proportion going from 0.04% -to 0.25% correlates to mental problems.
Even if the watch could sample atmosphere directly, is it sensitive enough to detect a shift from 21.00% -> 20.79% oxygen?
As it's estimating oxygen in the owner's blood, it might not detect anything different at all... not if the owner's body has already compensated by breathing harder or by "underclocking" their brain to make dumber decisions.
by Terr_
7/4/2026 at 8:15:06 AM
> The article references a study where the CO2 proportion going from 0.04% -to 0.25% causes mental problems. In other words, a difference in 0.21% of the air.I'm finding that pretty difficult to believe, to be quite honest with you.
And before you say "aha, carbon dioxide brain fog!" consider that I'm about a mile from the sea with a 40mph onshore breeze. This air is about as oxygenated as it gets.
by ErroneousBosh
7/4/2026 at 8:49:55 AM
It makes a lot of sense actually. You get severe symptoms when CO2 makes up only a couple % of the air. And can become fatal at like 5%. There’s not like a hard line where you suddenly die, it’s a gradual thing. It very much makes sense that we’d notice minor symptoms at a few thousand PPM when it only takes like ten thousand to feel it severely.by anon7000
7/4/2026 at 8:24:46 AM
1% (10,000 ppm) is enough for the person to become aware something is odd through drowsiness or an elevated heart rate.I don't think it's too far-fetched for a quarter of that to cause subconscious cognitive effects, that could be measured in tests.
by Terr_
7/4/2026 at 9:43:17 PM
The air in your lungs sits around 40,000ppm or 4% carbon dioxide.In every breath you remove about 25% of the oxygen from the air in your lungs, which is why mouth-to-mouth resuscitation works, at all. Most of the oxygen is still in there.
To be clear, that 25% represents a change in oxygen level from around 21% to around 16%, so the few tenths of a percent change in carbon dioxide just isn't a huge amount.
by ErroneousBosh
7/4/2026 at 1:20:31 PM
I got a monitor as we had an old apartment with bad ventilation. When I started feeling it I would check and it was always around 1200ppm and would open a window for a bit. Outside air is around 420ppm, but that's not the problem, enclosed and badly ventilated rooms are if you spend a few hours in there.by Hikikomori