(If this is OT please feel free to direct me to the required NG -
thanks).

I turned my mains power off yesterday at my consumer unit and was
suprised to hear my burglar alarm ringing from the outside. Its never
done this before. I though that if the mains went off (powercut etc)
then the battery in the system would power the alarm. When I restored
the power the alarm stopped sounding.

The battery cant be flat I presume as otherwise the alarm wouldnt
sound at all with the mains off. I took the battery out of the alarm
control box thingy and tested it with a multimeter. It showed approx.
12 volts so it cant be flat.

Any ideas?

CM.