AirValent CO2 Monitor First Thoughts

I’ve now had the AirValent CO2 Monitor for over a week. It’s still too early for me to share my full review (I am currently working on that!). I wanted to share a few preliminary thoughts on the device. Overall, it looks quite promising, and if you need the smallest monitor possible, this might interest you.

To begin with, let’s discuss the size and build quality. This device is tiny. I always thought the Aranet4 Home was quite compact, but next to this monitor, it’s immense! The AirValent monitor might not quite be half the size in every dimension, but it is significantly smaller in all dimensions, meaning its overall volume is much lower, and it feels half the size. The Aranet4 and Vitalight Mini CO2 Detector aren’t large but feel massive next to this monitor.

What surprised me a lot, though, was the weight. While this monitor is small, it’s quite weighty for its size. It feels a bit like a premium smartphone - while I’m not sure of the exact materials used, it reminds me of the build of an iPhone with metal edges and a glass back (again, I’m not sure what it is made from, but the build quality feels great). These materials give it a surprising weight, and while it still won’t make much of a difference in your pocket, the device looks like it weighs a lot less than it does.

Regarding connectivity, the device can connect to your smartphone via Bluetooth. The app is quite solid, but there is room for improvement. For example, I would love to be able to interact with the graphs more than just zooming in or out. I wish it had a slider like the Aranet Home app that shows you the exact concentration at any given time. On top of that, I wish you could select the dates for which you want to export data for (similar to the SmartAir CO2 Monitor). These are small issues, and I haven’t encountered any major issues with the app, but right now, it’s a good app. With a few small improvements, I think it could be great.

When it comes to accuracy, the monitor performs well, but it has a few caveats. Where most monitors on the market use the SenseAir S8 or Sunrise, the AirValent monitor uses a sensor from Sensirion. Now, this is not an issue because Sensirion is also a company that produces very high-quality sensors that you will find inside monitors such as those from CO2.Click and SmartAir. However, I have had a few interesting findings with this particular model, which utilises an SCD41 photoacoustic sensor from Sensirion.

In some comparisons (which are far from scientific), I found the SCD41 inside the AirValent monitor to be very similar to the Sunrise sensors in a couple of Aranet4 Home monitors. However, it also seems to be influenced by external factors as sometimes it consistently reads higher than the Sunrise sensors while at other times it consistently reads lower - and this seems to be directly related to whether I have the AC on or not. This is likely due to either temperature or sound (as it’s a photoacoustic sensor). I’m currently doing more testing to see if I can isolate the variable causing this difference or if it’s just a coincidence.

These are far from scientific findings, but I am continuing to look into this matter. Currently, I am testing 3 SCD41 devices alongside two Aranet4 Home monitors in an airtight container to rule out CO2 concentration as a variable. This is a bit of a rabbit hole, but now I am interested!

This isn’t to say the SCD41 or AirValent monitors are inaccurate—in fact, in normal conditions, they look to be very accurate (using the Aranets as a baseline). Even at extreme temperatures, they’re quite accurate; however, they do seem to vary more than I would have expected. I’m hoping to share more data and a full review in the coming days, so please subscribe to this thread if you’re interested!

So far, I’m really enjoying having such a small monitor with decent battery life. It’s so convenient that I can take it anywhere, and unlike the Aranet4, which is slightly too large for my pockets, I never question whether this is worth carrying. While I will delve deeper into what is causing the differences in readings compared to the Aranet4, it has been performing well and is overall accurate - especially considering its size

An update on this:

Unfortunately, the SCD41 does make some compromises for the sake of size.

Throughout my testing, I found that it sometimes recorded significantly higher than the Aranets I used as a baseline. After further testing, I found that the sensor became less accurate as the temperature increased. At moderate temperatures (< 30 degrees Celsius), the difference was usually less than 100ppm. However, at higher temperatures ( < 40 degrees Celsius), this difference reached up to 200 compared to the Aranets that I was using as a baseline (they are the closest I have to a reference monitor). At room temperatures 18 - 25 degrees, this issue was negligible.

After doing some research, I found that this appears to be common across photoacoustic sensors, and temperature can lead to signal loss. Is this an issue? I guess not for most people. Since most of us use carbon dioxide monitors inside, it’s unlikely the monitor will often be exposed to high temperatures that cause inaccurate readings. However, it is something to be aware of. At room temperature, the device compares very similarly to my Aranets - just be careful if you take it outside during summer or into hot environments.

Also, you need to be careful when calibrating this sensor. Any airflow and even cold temperatures can influence it, so you will want to ensure you take it outside for around 30 minutes and place it in a sheltered and warm area when calibrating.

I’ve now finished my review of the AirValent CO2 Monitor, which you can find here: AIRVALENT CO2 Monitor Review - The Smallest Carbon Dioxide Monitor. While the SCD41 does have some issues, it performs well at room temperature, and therefore, this device is still a solid choice if portability is key. However, this has caught my attention now and I plan to do further testing to see what I can discover about the sensor and to also see how it performs over a longer period of time (compared to the Aranet4 and some SenseAir S8 sensors). I will be back with updates once I’ve had some time to run further tests!

Here is a thread to a look at the SCD41 issues: