LP detector alarming for no apparent reason

LP/CO detectors that alarm with no actual gas leak are frustrating but usually explainable: they're sensitive to certain aerosols (hairspray, some cleaning products), low battery voltage on some models, or they've simply reached end-of-life (most have a 5-7 year lifespan even if they seem to work). Before assuming it's faulty, rule out anything you sprayed nearby and check the unit's manufacture date, usually printed on the back. How old is the detector?