There are three different detectors. The one at the bottom is for propane, and usually is attached to the 12 volt system. Then there is a detector for CO and a fire alarm, sometimes combined.
I like having at least two additional combined smoke/CO alarms, and changing out the 9 volt batteries every time change.
The propane one, I understand that it can get annoying (I woke up to it going off when voltage was low.) There are combined propane/CO gas detectors. I'd buy at least one of those if I were to disconnect the main propane alarm. That way, it won't be keening in the middle of the night, but one has protection.