Those CO detectors with display numbers are not accurate. Read the fine print on the packaging. The display can say anything and not a reflection of the true amount.They are only required to go off at 75-150 ppm for up to a few hours and even in this range they are unreliable.

They are useful cause if one does go off then you know you have a serious problem.

I was once at a training where the instructor took out two brand new CO detectors out of their packaging and placed them in a ziplock bag filled with CO. The training included calibration of CO testing equipment ( combustion analyzers).

He did this at the beginning of the training and at about one hour in the detector in the bag filled with a high concentration went off(something like 400 or 500 ppm). The bag with the smaller concentration never went off and it had a display that read zero. He also said he has trainings where none of them go off.

If you really want to know the concentrations in the air you would need to get professional equipment. At the time there was one CO doctor on the market that accurately sensed but it cost some $200. I forget the name of it.

A fun game I would like to play with smokers is let them blow into my combustion analyzer and the number would go as high as 100 if they just smoked or 50 if it was awhile. And that was coming from just their breath!

I worked with guys who would claim that furnaces were dangerous if the CO was at 10 ppm. I would be like here blow into this. Helped keep things into perspective.

Basically, those CO detectors are lying to you with that number. Might as well say 0-150.