With how bad air quality has been this year, I grabbed myself a DIY AirGradient kit so I can monitor air quality in my living space. It was easy to assemble and only required a little bit of soldering knowledge. I'm definitely not proficient enough at soldering as many components ended up crooked on the board. Still works though lol.
In the picture it's running ESPHome with the configuration from ajfriesen on GitHub.
I've been curious about getting a CO2 monitor after I heard that excess CO2 in rooms cause your brain to get dumber. I can't think of what to call it, maybe the CO2 talking.
(And just to be clear, I'm talking about CO2, not CO, we have a CO alarm.)