On Mon, 7 Oct 2019 19:38:11 +0100, alan_m wrote:

Um, you do know that the external sounder and strobe are
additionally
powered by a second non-rechargeable battery?

My bell box has a rechargeable battery that is also trickle charged in
my wired system via the alarm panel. My bell box also has red flashing
LEDs so a self contained non-rechargeable battery may not last that
long.

The bell box is normally powered from the panel to keep rechargeables
charged or flash pretty lights. It also "holds off" the sounder
and/or strobe. If the panel voltage drops to low, the sounder and
strobe trigger and run from the battery in the bell box. Once this is
triggered I'd expct it to run for several minutes before trying to
reset and retrigger if the panel volts are still low/abscent. You
don't want a scrote to be able to shut up the sounder simply by
feeding it volts from another source...

The tamper circuit in a bell box is often a spring loaded mechanical
switch which when the box is removed from the wall is activated.

And hopefully the cover... this should trigger a full tamper alarm
condition. Which may or may not cause the sounder/strobe to be
triggered.

Once triggered by a power cut the alarm can be disabled and run normally
from the old battery which you suggest has a voltage too low to run the
system.

Voltage too low when the sounder and strobe are drawing power...

--
Cheers
Dave.