*chirp* in the first 2 seconds of the video. We have a hallway chirp crisis in this country.

I keep extra batteries for my smoke alarm just so I won't have to listen to that incessant chirping that is worst than a nagging wife. It's funny but those batteries seem to run low at the worst times...at night when you're in bed. I just take the whole gadget off the ceiling and fix it in the AM.