Dave Plowman (News) wrote:
In article ,
William Sommerwerck wrote:
Lead-acid batteries are commonly used in such applications. My alarm
system uses one as a backup in case the AC fails.

They're common in the panel - but all the ones I've seen inside the
external sounder or 'bell box' are Ni-Cad or similar. But purely to make
it more compact, I'd guess.


A lot of modern bell boxes contain a battery which energises the
bell/siren in the case of attack i.e. cutting the wire to the box. This
is in addition to the back up battery in the alarm panel.

Ron(UK)