Tail, if I remember correctly, CO detectors should be installed at locations other than on the ceiling, which is the opposite of a fire detector. I think CO is heavier and tends to accumulate from the floor up, rather than the ceiling down like smoke.
Smoke detectors come in two varieties, a true smoke detector that works by reflection or obscuration, and ionization detectors that detect ionized particles from combustion. The smoke detector is prone to problems from cob webs, dust and insects while an ionization detector can be triggered by an air current, like the steam/hot air escaping from a ba
throom after a shower. Ionization detectors usually work using a low level radio active isotope, harmless level, but need proper disposal.