Who else has a CO2 (carbon dioxide) meter? If you just have one, (there are many under $150 on Amazon) how would you know it is accurate?
Organize a CO2 meter users club meet up and compare readings somewhere outdoors. If you can get three or more and everyone else reads around 418 ppm (parts per million) and your own meter says 1200, you will know your sensor may be failing.
You’d likely need just a 15 minute window, it should be pretty quick and obvious. First just check interest in your city, for all with a CO2 (carbon dioxide) meter who are interested, then you might use a group meeting tool like doodle.com or lettucemeet.com to find when the most people are available.
Note: This is not for CO (carbon monoxide) meters, that’s a different club.