the level of CO2 is dependant on a few things. but the room level will be elevated with occupancy.
This has been used by building automation companies for decades.
if you have a motion detector, that will react qucikly. but, once you stop moving, you are still expiring CO2 so the room level will increase
the level will be dependent on the HVAC system, if it is forced air, then the level will be lower than if it is floor or baseboard heaters.