I have an Airthings Wave. It does CO2 along with a couple of other things.
I really like mine. It helped me discover that I was sensitive to volatile organic compounds: every time I felt the air was stuffy inside my apartment, it corresponded to a VOC peak that was happening right then.
The one downside to the Airthings Wave is that it looks like hospital equipment. Grey, lifeless plastic pill design that was probably outdated even in the 1970s.
Love mine. I think it looks fine, has a simple display to display a few values, white, and nicely rounded. Basically invisible. I use it to collect the info so I can look at the graphs as needed.
Seems like a really nice design. I was impressed that bluetooth LE was enough to connect reliably across 3 floors (with the gateway on the middle floor) of my house. The view plus automatically acts as a hub if you plug in USB for power, but falls back to batteries as needed.
All in all just about perfect, it works, easy to setup, and collects tons of data (Radon, PM2.5, CO2, Humidity, Temp, VOC, and pressure). I do wish it collected carbon monoxide though.
I'd second the Airthings device, they have pretty high quality sensors and include VOCs, CO2, pm2.5, radon, and a few others. A little bit pricey is the only downside for me.
It works well enough and home assistant integrates with it. I cannot comment on it's accuracy since I've never owned another CO2 monitor as a reference. However, it is very responsive to the various things I've tried to manage CO2 in my bedroom - such as opening the windows to differet degrees, position of my curtains etc.
I have the Qingping Lite[1] which is a well-made device (and can run on batteries if you want to take it somewhere to check things out). After updating the firmware and calibrating it outside it seems pretty consistent - though I was mostly interested in it for CO2, I have a Flow 2 which doesn't agree on PM2.5 or PM10 with the Qingping, I suspect that the particulate sensor in the QP is not the best, it always seems to read low.
You will not be able to get something of higher value than that, because technically it's a demonstration device and likely doesn't make them much if any profit.
Maybe, but the calibration aspect to this device makes it a bit impractical.
The thing needs to be powered on and taken outside every so often for calibration, who does this for residential use I'm not sure but for most with busy lives I don't think it's a great idea.
If it is powered off at any time it needs to be done again if I'm not mistaken.
They will apparently include calibration options in the next firmware update.
And it's not as much as of a hassle as first appears. After a week you can expect readings to drift downward by 50-200 ppm depending on whether or not you aired out the room at all - and it's a one time thing, won't happen continuously every week. Then you just take it outside and it will be fixed in under 10 minutes (<400 ppm reading trigger auto calibration immediately).
I'm not confident that the other co2 meter options are in any way better. They most likely also do auto calibration but don't tell you. Counting on the fact that most people won't notice the drift.
I really like mine. It helped me discover that I was sensitive to volatile organic compounds: every time I felt the air was stuffy inside my apartment, it corresponded to a VOC peak that was happening right then.
The one downside to the Airthings Wave is that it looks like hospital equipment. Grey, lifeless plastic pill design that was probably outdated even in the 1970s.
If you ignore how it looks, it works fantastic.