There may be some confusion here. The detector that is low down, near the floor, is a propane detector, not a CO detector. Propane is heavier than air and settles near the floor.
The CO detector is near ceiling level, usually in the bedroom. The CO detector is battery powered, as is the smoke detector.
The propane detector is powered from the trailer battery. The power for the propane detector bypasses the shut-off switch so that it is always powered. That is because the sensor in the propane detector deteriorates if it is powered off and on once it is put into service.
Large concentrations of paint fumes can poison any of the detectors. I ruined my CO detector by using a spray can in the trailer.
John W. Irwin
2005 Classic 28 "Sabre-Dog III"
2013 Silverado 2500HD Duramax/Allison LTZ
WBCCI #9632, TAC TX-10