Floating around this week is this video https://www.youtube.com/watch?v=1Nh_vxpycEA wherein a person sits in a sealed off cube full of plants and carbon dioxide monitors, with an EMT on the other side for safety - the person claims that 300 ppm of outside air was fresh, and now 400 ppm is fresh - but that indoors, it can easily climb to over 1000ppm and that there might be a significant cognitive decline associated with it.

I was looking for a nice wall receptacle for a hallways that measures carbon dioxide inside my house because I will go for weeks at a time without getting a proper air-out. In northern new england, honestly, it could be months for all I know. Only a few random door openings and the leakiness of the house are my exchange.

I don't know how accurate their claim is, and it's certainly a universal solvent to consider stale air is the reason a person is behaving a way. Measuring the levels and being aware of it seems worth 60 bucks, if it's actually a factor in our rationality.