I have a built in clock next to the bed in my motorhome. Happens to have an alarm on it. For some reason, sometime after I turn on the furnace, it begins to sound its alarm. Must be some crossed wires. If you have a built in clock you might want to check that.
Some time ago, my LP detector sounded an intermittent alarm when my coach batteries were going bad. That smell, not just propane smell, can set off the LP detector.
Guess I would try to get my ear to any of the detectors (smoke, LP, carbon monoxide) or built in clock if it exists, as soon as you hear the sound.