[Havoc]

Have a similar setup. Unfortunately the open a window thing isn't all that reliable as test. Even sensors cheaper than the SDC40/41 will happily do that.

The issue is more drift and that its a very localised measurement. The sharp spikes in the graphs are often more about the air is moving than the room's total CO2 changing. Like on mine (also sdc41) I can see when I wake up on the bedroom one. Being awake produces more CO2 sure but it's marginal. 80% sure the spike is simply more turbulence in room. Lying still for hours vs getting up and making bed etc