Good article on CO detectors;
CO detection
Canadian, but applies to all in-home detectors sold in N. Am.

This thread sounds like hydrocarbon gases and CFC's are being confused with CO by some people. CFC's here have a very strong odor (added) so a leaking fridge is immediately detected.

The gas company checks for HC-leaks here (natural gas) every time the meter is checked; an Underwriters Lab CO detector is required here, as well as the usual smoke detectors.
I remember propane tanks for heating, many years ago when I was a student living in a converted garage, but haven't seen any for years, so can't give any advice.