[scosman]

CO2 can also reduce cognitive capacity. It's useful to monitor, other than just being a proxy for air quality.

Sidenote: it's a fun project to built your own. You can buy the good sensor from this test (Senseair S8) for about $20 from AliExpress. Add a ESP32, a case, and EspHome.io software, and have a high quality sensor for <$30. Same quality as the Aranet4 device you mention, at about a tenth the price. They also use a senseair sensor with the same accuracy rating, but slightly higher priced one designed for long term use on a battery.

[aftbit]

I tried this but somehow my sensor got stuck at 500 ppm and never recovered. My Airgradient devices have not yet suffered from this problem.