I've been using the uHoo air monitor for the last few months. I have one in the bedroom, living room, and office. It monitors many air factors, but CO2 was my primary focus.<p>My original goal was to have a fresh air intake activate automatically at certain concentration levels, if the outside ambient temperature/humidity were appropriate.<p>However, living in a hot humid place, the data I got made that solution seem futile. Ventilation for CO2 alone takes so much air that it becomes basically a full reset on dehumidifying and conditioning.<p>However, this failure lead me to the fortuitous discovery that by adding 36 hydroponic heads of lettuce, I am now going <i>beyond</i> outside CO2 levels, dipping down to 390-400 and only reaching ~700 overnight when it's the worst.