snip
It transpires that most alarms have a big capacitor in the sounder
box. This activates the sounder if the alarm is tampered with eg
having the cables cut or the cover removed. I seem to recall that it
took about an hour before the capacitor drained down. I wasnt too
popular with the neighbours.

Question now, as you might expect, is how does one get round this as
the cable has to be cut and extended so that it can re re-routed?

An important safety tip if you intend to remove the bell box cover while up
ladders and are unsure whether it will sound due to being tampered.

You will be very close to the sounder and up ladders and, close up, it
should be very loud.

Your hands will probably be full too.

You natural involuntary reaction will be to draw back.

There have, I seem to recall, been instances in the past where the shock of
the high intensity sound has caused the uninformed D-I-Y alarm engineer to
fall off their ladders.

Just be aware and prepared for the acoustic shock and don't fall from your
ladder.