[rale00]

Sounds like the meter was broken or at least wasn't properly calibrated. CO2 level should drop off quickly with a window open.

[AlexandrB]

I think so too. Use to work with a lot of CO2 sensors in a previous job and it's very difficult to keep an elevated CO2 level going if there's any exchange of air with the outside.

[lstodd]

Yeah, this. 1000ppm is very noticeable, true 2000 is unbearable.

Living in a center of a city next to a 10-line highway opening a window drops a properly calibrated sensor into 400s inside a few minutes.

[_Microft]

She brought the meter outside where it measured 480ppm.