I have one on my unheated garage door @ 9800 feet up in the wintery rockies of colorado.
That reminds me - we were camping in Winter Park last week and as I'm lying there I started to wonder if you could set up a security perimeter around your campsite using motion sensors and an X10 security system?
I mean - scatter some motion sensors around and wait for a bear to waltz into your campsite.
I guess I'd just have to hope that the siren going off scares him, rather than give him a reason to bite into *that* tent.