as the others have said, your 12v battery is the most common cause, if you don't install a battery disconnect switch or take the battery out or don't keep the shore cord plugged in.
the propane detector is just one of the many parasitic power drains that RVs have.
a bad detector is a much rarer cause, but it does happen.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC