As I understand it, the rear one shuts off after 10 minutes (30 perhaps) but the front stays on. I came out to a dead battery because I had left my detector plugged in and turned on for a couple of days.... I've since had it hardwired, and not had a battery problem again.... (well, the battery in my remote keeps going dead since I ran it thru the washer and dryer a couple of times, but that's a different issue)