We have a propane
alarm near the floor and a smoke alarm near the ceiling. I installed a carbon monoxide alarm 2/3 the way up from the floor and it has been such a problem that I have disarmed it.
It seems to work well during low temperatures, but once the summer heat comes it goes off often and registers elevated CO counts. This is when the trailer has NO combustion of any kind taking place, so it is not CO that is setting it off at all but other fumes in our 8 year old trailer (which should have pretty much have off-gassed most of what originates in its building materials).
In checking with my brother-in-law who is a fireman he said that he does not have a very positive attitude about the CO detectors since they very often give off false alarms and therefore cause more trouble than they are worth.
I thought I had a faulty example, but this gives me pause to think they are inherently unstable.