Hi
I want to be able to connect smoke alarms to my existing house alarm. At my
local alarm shop they sell a small pcb which replaces the 9v PP3 battery and
allows the smoke alarm to be connected to the main alarm. This pcb probably
has a voltage regulator on it (12v to 9v) and some sort of current sensing
to trigger the main alarm when the smoke alarm sounds.
What I want is to be able to make this pcb myself as the shop wanted to much
for it and a want a few of them, does anybody know a circuit for such a
thing?

Cheers
John