You may for peace of mind want to test the Fluke CO-220. This can be accomplished with a few common items.
Fluke CO-220 Field Test
Require items:
Matches, Lighter, or other flame source
Coffee cup or other simple container
1. Invert the coffee cup so the opening is straight down.
2. Light the flame source under the inverted cup and wait a few seconds.
3. With the CO-220 turned on wave it under the cup. This should produce a simple reading within the range of the CO-220 (1-1000 ppm).
Note:
Under no circumstance is acceptable to test against a vehicle tale pipe. This will foul the sensor rending the unit uselss.