It was slightly ajar in the wall, still powered on though. Pushed it in further. Started chirping. Took it out to see what was going on and try to stop it (because it was in the room with someone who is sensitive to loud noise). Then this insane "tamper" constant alarm starts shrieking (and it sounded WAAAAY louder than 85 dB) until we finally plugged it back in and reset it.I hate to think what would happen if there's a power outage. A backup battery is meant to keep it working when off AC, not to make it sound like being off AC is worse than CO gas itself.