On most RVs the LP leak detector is hardwired to the house battery, but, the smoke alarm has it's own battery; usually a couple of AA. The chirp is telling you to change the internal battery...
If you pop it off its base, you should see them on the backside. As for how it "pops" off, depends on the type; some pull off, some have a catch on the side and then it levers off and others twist off their base.
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