It doesn't actually have to be the CO2 per see. It can be used to measure overall air and ventilation. Or how many humans there are in a house/room, and if they

It doesn't actually have to be the CO2 per see. It can be used to measure overall air and ventilation. Or how many humans there are in a house/room, and if they are asleep or awake. The drowsiness is probably due to both low oxygen levels and high CO2 levels, and more.