We have a burglar alarm with a couple of spare "zones".
Unfortunately, when we had our fire alarms fitted (mains powered and
all interlinked)

snip

(It detects this by the increased
current draw of the smoke alarm siren.)

snip

You can still get them. Bottom of this page

http://www.hoyles.com/acatalog/inter...ys-timers.html

I assume this requires the main supply to the alarm to be removed else
the unit won't (or might not) see the current draw. But does it work
with just one module in one of the interconnected alarms? I can't see
why it would not but there's a lot I can't see.

(Not a hypothetical question as I've got interconnected mains powered
Kidde smoke/heat alarms and plan to fit a burglar alarm next year.)
--
Robin
PM may be sent to rbw0{at}hotmail{dot}com