It sounded like the fire alarm at my apartment complex. I know what that sounds like because we had a (apparently false) alarm a few months ago.
Now I started to get a little anxious. My computer is in the apartment, and so are all of the backups. So are my savings bonds, and the backup for the bonds is on the computer. Eeek!
Soon thereafter, the fire alarm stopped, and as I passed the complex just before mine, I saw the fire truck parked in their lot and no obvious signs of smoke or flame in the area. I guess our neighboring complex uses the same kind of alarms as we do.
I'm reminded of ConAdian in 1994, when the fire alarm went off one night. After the late evacuation, I stood in the rain chuckling. Someone asked why I was laughing.
I said, "It must be a false alarm. The Site Selection money and ballots are all locked up in the hotel's safe-deposit box, along with my passport and other critical papers. Otherwise, the hotel would burn to the ground." (We were let back in shortly thereafter. I heard later that the rain had caused an electrical short that set off a smoke alarm, but no real harm came of it. I suppose some of the people in the Place Louis Riel hadn't even gone to bed yet, that being one of the two "hospitality" [party; the hotels were allergic to that word so we had to use the euphemism] hotels.)
I think I really do need to buy a small fireproof box for the savings bonds and to hold backup disks.