A customer called us recently from inside their indoor greenhouse in Colorado. They had just installed a CO2 detector (carbon dioxide, not carbon monoxide there's a difference) hooked up to an alarm. Their question was very simple:
"How do I know if the CO2 monitor and alarm is working?"
Fortunately, the answer is simple: take a deep breath, hold it for a moment, then blow it directly into the meter's air vents. Repeat this several times.
Exhaled breath is approximately 4% (40,000ppm) carbon dioxide which is enough to activate any CO2 detector, CO2 monitor or CO2 safety alarm.