[jadams5]

I got this model several months back and have been really happy with it: https://smile.amazon.com/gp/product/B01FYWU2IS/

I got it to monitor CO2 levels in a house without central air. It's pretty amazing how quickly it rises without the air on or a window open. If the air in a room feels "stuffy", it's probably over 1000 ppm.

[JohnJamesRambo]

Yep, that's the one I have. It's fantastic.

[amelius]

It says the CO2 range is from 0-5000 ppm, but exhaled breath has a much higher concentration (according to another comment). Are you able to accurately measure the inhaled concentration in case the breathing happens in a confined space (e.g. helmet or under a blanket, etc.)

[JohnJamesRambo]

I don't use it for confined spaces, so 5000 ppm is plenty for me. If any building I am in is over 5000 ppm I need to leave immediately!

https://www.burntec.com/images/co220b.jpg

[sigstoat]

in the unlikely event someone manages to shove that thing inside of their helmet, do they _need_ an accurate measurement? if it hits 5000, it can just be read as "way too much".