AirSpot Review – A Tiny Carbon Dioxide Monitor That Can Be Worn as a Watch!

Many of us who follow carbon dioxide monitoring have long wondered when sensors will be small enough to fit into a smartphone or smartwatch. That day might still be a while off, but sensor technology has come a long way over the past few years, and the results have been impressive. Sensors like the Sensirion SCD4x (and the even newer STCC4) series have made it possible for CO2 monitors to shrink down to sizes that would have seemed impossible not too long ago. Unlike transmissive NDIR sensors, which measure light and have physical size constraints because of it, photoacoustic sensors like the SCD4x measure sound, and that’s what makes them so much more compact.

When I first published this review almost exactly one year ago, the AirSpot CO2 Monitor was the smallest all-in-one CO2 monitor I had come across, and that’s still the case today. There are a handful of smaller options out there, but they tend to lack an internal battery, connectivity, or both. The AirSpot has all of that, and on top of it, you can wear it as a watch with the optional strap. While I don’t use the watch strap myself, it’s a cool choice to have.

What also makes the AirSpot interesting isn’t just the size, though. It’s the whole ecosystem that has been built around it. With the optional accessories, you can mount it to your phone, clip it to a keychain, or wear it on your wrist, and that range of options (combined with the app) turns the device into one that you can actually build into your daily routine quite easily. For a CO2 monitor to be useful, you need to have it with you, and the AirSpot makes that much easier than most.

A lot has changed since I first wrote this review, though. I now own two AirSpot units and have been using them regularly for over a year. The hardware has gone through a small update to the materials, and the app has changed significantly (but more on that later). What I didn’t anticipate when I first reviewed this device was just how much I’d come to rely on it. It’s now the second most-used CO2 monitor in my rotation, behind only the Aranet4 Home. Part of that comes down to size, but a big part of it is the app, which has become the most powerful CO2 monitor app on the market, and that’s what I want to dig into with this updated review. Let’s dive in!

Accuracy

The AirSpot CO2 monitor uses a Sensirion SCD41 photoacoustic NDIR sensor. This ultra-compact sensor shows up in a few other small CO2 monitors too, like the AirValent CO2 monitor and CO2 Click Model F. It’s a trusted sensor from a reputable brand, and when calibrated correctly, it performs well. That said, it does come with a few caveats, which I’ll get into below.

The stated accuracy from AirSpot is ± 40 ppm ± 5% of reading, though this is essentially a worst-case figure. Sensirion’s own specification puts the SCD41 at ± 50 ppm ± 2.5% of reading below 1000 ppm, and ± 50 ppm ± 3.0% above that up to 2000 ppm. The ± 40 ppm ± 5% figure only really applies at concentrations above 2000 ppm, which you’re unlikely to hit outside of very specific circumstances. With that said, I appreciate AirSpot officially listing the worst-case specification.

For this updated review, I carried the AirSpot on a keychain alongside a second AirSpot unit, an Aranet4 Home, and an Atmotube Pro 2 for over a month. These devices went everywhere with me, so it was a pretty thorough real-world comparison. As the graphs show, the AirSpot tracks very closely with the Aranet4 Home. The two trends are essentially identical (with a near perfect r-squared), which reinforces that this is a capable sensor.

Above is a snapshot of the overall test. If I show the whole month, the graph becomes far too difficult to read!

I should mention that the Aranet4 Home used in this test was freshly factory calibrated, while the AirSpot had automatic baseline calibration (ABC) enabled throughout. With ABC on and the device frequently being taken outside into ambient air, it did consistently read a little high. But the offset is very systematic, which suggests it’s a calibration difference rather than any real inaccuracy. If both devices were calibrated together, I’d expect the readings to match almost exactly.

The over reporting was very systematic.

It’s worth noting that I actually ran this comparison specifically to look at how ABC affects readings over time, which is a useful thing to understand if you plan to use the device in environments where it gets regular outdoor exposure. If you would like to learn a bit more about ABC, please read the explainer below which goes into more detail.

One thing the SCD41 is sensitive to is sound, and this can occasionally cause single-reading spikes in the data. In my earlier testing, I saw these fairly regularly, and they were hard to miss. The monitor would sit steadily around 1000 ppm (for example) and then log a single reading of 5000 ppm before returning to normal. In my experience, this happened most often when the device was in my bag.

After raising it with the AirSpot team, they confirmed that sound is likely the cause, given how exposed the sensor is inside the device. I’ve used other SCD41-based monitors and never seen spikes this pronounced, so the level of venting around the sensor does seem to make a difference. The good news is that this appears to have improved with recent firmware updates, and I’m told the team continues to work on filtering these out algorithmically. They’re easy enough to identify and ignore, but it’s still worth knowing about.

The images above show some of these random spikes. During all of them, the device was in my bag, and there were no other actions that would account for these spikes at the given times.

Overall, the SCD41 is a widely trusted sensor and the AirSpot performs well with it. It’s not going to match a high-quality transmissive NDIR sensor outright, and the photoacoustic design does come with some trade-offs, but no transmissive NDIR sensor can match this form factor. That’s the core appeal, and the accuracy is more than good enough for real-world use.

One final note before moving on: the app also gives you quite a bit of control over how the sensor behaves. You can set the reading frequency anywhere from every 5 seconds to every minute, every 3 minutes, or even switch to manual-only readings if you really want to stretch the battery. ABC can be turned off entirely if you prefer, and there’s also the option to add a manual offset when calibrating, which is something I really appreciate.

My local ambient concentration is 429 ppm!

Most monitors assume 400 or 420 ppm as the outdoor baseline and calibrate to that regardless of where you actually live. With the AirSpot, you can check your local ambient concentrations and calibrate to that specific value instead, which makes a real difference if you’re somewhere with slightly elevated background CO2. For those living at high altitude, the sensor doesn’t do automatic air pressure compensation, but you can enter a manual correction in the app, so it’s covered.

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Design

AirSpot (left) and AirValent (another tiny monitor).

The AirSpot carbon dioxide monitor is a very compact device, smaller than any other all-in-one CO2 monitor I’ve come across, including the AirValent and AirValent TravelLite. Don’t get me wrong, both of those are still small (especially compared to something like the Aranet!), but the AirSpot takes size to a new level. As far as I know, nothing else on the market combines this footprint with a built-in battery and wireless connectivity, and that remains a unique selling point.

That size is also what makes the accessory ecosystem possible. You can use the AirSpot as a standalone handheld device, attach it to a keychain, mount it to your phone or a wall, or wear it on your wrist with the optional watch strap. The phone mount works with adhesive tape on one side, so it can go almost anywhere. I’ve got one stuck to my wall, and I use it as a docking point for one of my AirSpot devices when I’m at home. After extended use, I’ve settled into mainly using the keychain and occasionally the phone mount. I tried the watch strap too, and while it’s a fun option, the device is too big on my wrist for everyday wear. Still, having the option is nice.

The keychain is actually my favourite accessory by some margin. It adds a bit of protection to the device, and it makes it incredibly easy to clip onto a bag or backpack and just take it with you. That convenience is a big part of why this has become one of my most-used monitors. One thing to keep in mind, though, is that the keychain does make the device slightly bulkier (it also comes with a mounting clip), so it’s a little less pocketable. I’d still recommend it, but think about how you plan to carry the device before buying every accessory at once, because they’re not cheap for what they are and some people won’t get much use out of certain ones.

In terms of build quality, my first impression wasn’t great. The device and accessories feel quite plastic, and the finish doesn’t exactly scream premium. Part of this is a deliberate trade-off, though, because the AirSpot weighs almost nothing at just 17 grams, and that’s only possible with lightweight materials. A heavier wrist strap or keychain would undermine the whole point of the device, so it makes sense even if it doesn’t feel luxurious. But… I can’t help but still think the device and accessories feel a bit cheap.

Late last year, the device also received a hardware refresh that made it slightly more durable and, importantly, added support for USB-C to USB-C charging. Previously you were limited to Type-A to Type-C cables, which was a real inconvenience for anyone who has moved away from Type-A entirely (like such as myself). Having a CO2 monitor that finally charges over a modern cable is something I appreciate a lot.

Despite feeling a bit cheap, after extended real-world use, I can say my older device has held up reasonably well. There are a few scratches on the screen and back, but they’re not as obvious as I’d have expected given the build quality, and visually there isn’t a huge difference between my older and newer unit. I do hope the materials continue to improve, but it’s fair to say the durability has been better than my initial impressions suggested.

Moving on from the build quality, the device itself is small but still manages to fit a USB-C port, a home button, and a decent-sized screen. The button has a satisfying click to it and is easy to press despite being compact. Along the sides and bottom are vents that allow air to reach the sensor, which is standard across all CO2 monitors. It does mean the device isn’t waterproof, so it’s worth being careful, especially given how portable this one is. A monitor that lives on your desk is unlikely to encounter rain. One that lives on your keychain is a different story.

The screen shows the current CO2 reading, a historical graph if you have that enabled in the app, the time, battery level, and a few status icons. By default it stays off and wakes when you press the button, which I’ve kept as my setup because it does a lot for battery life. Even with the screen off, the device keeps taking readings and syncing to your phone over Bluetooth.

Speaking of battery, the AirSpot does surprisingly well for such a small device, and how long it lasts depends almost entirely on how you configure it (on a side note, I appreciate having this flexibility). At the most intensive setting, taking a reading every 5 seconds, you’re looking at around 12 hours. Step that down to every minute and you get around 6 days, which is what I run mine on. At 3-minute intervals you can stretch that to 10 days, and if you switch to on-demand mode, where CO2 is only measured when you manually request it, you’re looking at up to 21 days. If you turn the device off entirely between uses, the battery can reportedly last up to 5 months. For most people, the 1 or 3-minute interval will be the sweet spot, and in my experience the real-world battery life at those settings has been at least as good as advertised, often a little better.

Overall, despite not having great initial impressions, I’m quite happy with the design of the AirSpot CO2 monitor. I’ve used it every day for well over a year now, and it’s grown on me. While many CO2 monitors share a broadly similar design, I appreciate some of the things that make the AirSpot stand out, like being able to see historical data right on the screen. It’s a small touch, but it’s the kind of thing you end up using more than you’d expect.

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App & Connectivity

When I first received the AirSpot monitor, the app was admittedly far from great. That’s changed significantly. The team has pushed major updates over the past year, and what’s in front of users now is a genuinely different experience. If you owned an AirSpot previously and gave up on it because of app issues, I think it’s time to give it another look.

Pairing is straightforward. Since the connection runs over Bluetooth, you just need to make sure that’s enabled on your phone, and the device shows up almost immediately. Once paired, the app’s home screen offers quite a bit more than you might expect, including a devices menu, the CleanAir map, settings, air quality improvement resources, and news related to indoor air quality. It’s clear from the range of features that this app was built by people who genuinely care about the subject.

One thing worth understanding before diving into the app is how the AirSpot handles data when you’re not connected. Unlike most CO2 monitors, this device works very well as a standalone unit. It displays a historical graph right on its home screen, so you can check trends even without your phone nearby. It also stores up to a week’s worth of readings locally at 5-second intervals, which means you won’t lose data if you only sync occasionally. That said, the internal storage does have limits, so if you want complete records without gaps, syncing daily is the safer habit. I’ve learned this the hard way, including during the month-long comparison I ran for the accuracy section, where a few missed syncs left some frustrating gaps in my data graphs.

The devices tab is where you’ll spend most of your time. Here you can see your current CO2 reading, battery level, and request an on-demand measurement, which is a feature I’ve only come across on the Aranet4 Home otherwise. From here you can also pull up a historical graph, which is quite capable. You can zoom in and out across different time periods, add threshold lines for good, mediocre, and poor air quality, and overlay a percentage of rebreathed air as a third axis. Data can also be exported to CSV if you want to analyse it more closely. One thing missing from both the graph and the export, though, is temperature and relative humidity data, even though the sensor does measure both. Hopefully that gets added in a future update.

The settings menu is where the app really stands out. Almost everything is adjustable. You can set multiple alarms at different CO2 thresholds, and you can even configure one to trigger when concentrations fall below a certain level, which I haven’t seen on any other monitor. Screen behaviour, measurement interval, CO2 offset, display thresholds, and calibration settings are all customisable too. As I mentioned in the accuracy section, you can set your own calibration target based on your local outdoor CO2 concentration rather than assuming a fixed 400 or 420 ppm baseline like most monitors do. For a power user, this level of control is genuinely refreshing, and it’s the kind of thing that makes the AirSpot feel like it was designed by people who actually use these devices seriously.

The map feature has also grown since my original review. It now pulls in data from indoorco2map alongside the AirSpot community’s own contributions, so there are considerably more data points to browse. The team has mentioned wanting to develop this further into something of a central hub for CO2 data from multiple sources, which is an ambitious direction that I’d love to see come together.

My favourite addition to the app, though, is the native platform integration. There are live activities and a wide range of widgets available on both iOS and Android, so you can glance at your current CO2 reading without ever opening the app. I use this constantly. Some of these features can be a little temperamental on iOS, but in my experience that tends to come down to Apple’s own limitations around background app activity rather than anything the AirSpot team has done wrong.

The app also includes a section with news and resources on indoor air quality and steps you can take to improve it. The links take you out to the AirSpot website rather than keeping everything in-app, but the information itself is often useful and it’s clear a lot of work went into putting it together.

Overall, AirSpot has shown a real commitment to improving and expanding the app, and it shows. It isn’t the most visually polished app out there, but the depth of features and the responsiveness to user feedback more than make up for that. It’s become one of the more capable companion apps I use alongside any of my monitors.

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Pricing & Competition

The AirSpot CO2 monitor sits at just over $140 USD (but you can get 10% off with the code ‘BreatheSafeAir10’!), putting it firmly in the premium segment of the consumer CO2 monitor market. At that price, it’s competing with devices like the INKBIRD IAM-T1, Aranet4 Home, and AirValent CO2 monitor, all of which are well-rounded and capable devices. So the competition is real, and I don’t think it’s worth pretending otherwise.

That said, the AirSpot brings some things to the table that none of those devices do. Most obviously, it’s the smallest all-in-one CO2 monitor available at any price point, and if a compact, discreet form factor is important to you, that alone might settle the decision. Beyond size, it also combines features that are otherwise spread across different devices. The on-demand reading feature, for example, is something I’ve only seen on the Aranet4 Home, but the AirSpot pairs that with more customisable calibration settings and a more flexible app than any of the three competitors I mentioned. It’s a combination that’s hard to find elsewhere.

There are areas where the competition still has an edge. The Aranet4 Home offers Home Assistant integration, and all three of the comparison devices have E-ink screens, which the AirSpot doesn’t. Whether those trade-offs matter depends entirely on how you plan to use the device, and I don’t think there’s a universal answer. What I will say is that at this price point, all of these monitors do the essentials well, and the AirSpot is no exception. If anything, it goes further than most on the advanced user-settings side.

The one feature I’d still like to see added is the ability to view and graph temperature and relative humidity data. The SCD41 sensor measures both, so the data is there. It’s just not currently surfaced in any meaningful way in the app, and that’s a gap worth filling.

To wrap up, I think the AirSpot is fairly priced given what it offers. It’s a premium device, but not unreasonable. If portability is your priority, nothing else comes close. And even if you just want a capable, accurate CO2 monitor with a strong app and a lot of customisation options, it’s absolutely worth considering.

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Conclusion

A few years ago, I dreamed of a device like this. One small enough to slip into a pocket without really thinking about it. The AirValent is a small monitor, but it still adds a noticeable weight to your pocket. The AirSpot goes a step further, as it’s both smaller and lighter, to the point where I can put it in my pocket, backpack, or sling bag and genuinely forget it’s there until I need it.

What’s surprised me most over the past year, though, is how naturally the AirSpot has integrated into my daily routine. Thanks to the live activities and widgets, I often don’t even need to take the device out of my bag or pocket. I can see the current CO2 concentration right from my lock screen, which sounds like a small thing but makes a real difference in my case. Most monitors require you to actively check them, which adds a step to your routine that’s easy to skip. With the AirSpot, that barrier is basically gone, and I think a lot of people will find that useful.

I’m also a big fan of the accessory ecosystem. It’s not something you see from other CO2 monitor brands, and it gives the AirSpot a flexibility that no other monitor can match right now. I’d love to see the lineup expand over time. A protective case without the keychain ring would be a great addition for anyone who wants a bit more durability without too much extra bulk. But even with just the three accessories available today, the range of ways you can carry and use this device is very handy.

On the feature side, the AirSpot is well-rounded, and it needs to be at this price. It pulls together some of my favourite things from other monitors into one package, and the app has come a long way. The main thing still missing is the ability to view and graph temperature and relative humidity, which the sensor measures but the app doesn’t currently surface. That gap holds it back from being a truly complete package, but it’s something I hope gets addressed. Even without it, I can recommend this device comfortably, and I think it’ll suit a lot of people well.

If you’ve read through this review and still have questions, feel free to leave them in the comments below. I always try my best to reply. And if you’ve already used the AirSpot yourself, I’d love to hear your thoughts too. Thanks for reading!

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AirSpot CO2 Monitor FAQ