Skydancer
I, and others I've spoken to, think this is to warn us of a nuclear attack. Remember the literature in the 1980s? Take off a door and hide under the stairs and put the door in front of you? My DD says she can take her door off as she's just bought a screwdriver. Her problem is she hasn't got an understairs cupboard. We have though so, as she's only 10 minutes from me, I've suggested that if the alarm sounds she takes off the door and then runs down the road with it to my house. She should just have about time by my reckoning.
Oh that did make me laugh, Skydancer!
My grandparents used to hide under their grand piano when the air raid warnings went off. Luckily their home was never hit. Can't see it being of much use had it been.

