I bought a $30 CO2 monitor a couple months ago, and it confirmed my suspicion that my home office (a normal room about 12' x 18') reaches unhealthy levels over 1000ppm after just a few hours; opening a window quickly restores levels to the 400-700ppm range. Afternoon mental fatigue solved. Highly recommended.

Fantastic, did you go for a particular "trusted" brand or just went on vibes? How should one rationally approach shopping for a CO2 monitor for home office use?