CO is a product of combustion, and will therefore be hotter than the ambient air in most cases. The primary reason manufacturers say CO detectors should be a bi

CO is a product of combustion, and will therefore be hotter than the ambient air in most cases. The primary reason manufacturers say CO detectors should be a bit lower on the wall is to avoid false positives (well... not really false, just alarms for events you don't really need to worry about). A little CO emission is expected during the normal operation of gas/wood burning appliances. A CO detector at the ceiling might go off when it detects these little 'puffs' of CO. In practice, a CO detector should be averaging the level of a couple minutes, and not worry about short transient peaks (which is what I suspect the nest detector does). If you're in a fire, stay low and get out. Source: I'm a firefighter.