Just for grins I ordered this CO2 detector yesterday. The Amazon truck just dropped it off a few minutes ago. Calibrated it per the instructions. Indoor CO2 concentration in my office is under 900 ppm, very safe. It also displays temp, humidity, time, weekday and day of month. And is colorful. It is battery or USB-powered, but they just give you the cable, so you need a USB source unless you want to use the three AAA batteries, which they do not supply.
https://www.amazon.com/Newentor-Dete...27&sr=8-3&th=1