Chris Lewis wrote:
Situation: Found out that the home builder had put in AC smoke detectors
that weren't gang-trip. I installed new gang-trip ones, and decided to
put another in the detached garage.

Gang-trip 3-wire type (hot, neutral and trigger).

Occasionally, work in the garage (soldering something, starting the lawn
tractor etc) will set off the garage alarm which immediately fires up
the others... Annoys the rest of the family no end.

Suboptimal.

Been thinking of putting a switch into the garage alarm's supply feed.

Ideally, it'd be a normally-closed timer that when "enabled", it'd
disable the garage alarm and gang trip feeding the other alarms until
the timer ran out.

Has anybody else done something like this? Suggestions?

I could put a double-pole switch in (to cut the hot and neutral), or
even a single-pole (just cutting the hot should work), but these
are battery backup units, so I suspect that wouldn't work...

So maybe the best I can do is disable the gang-trip with a switch.
Are there any cheap "normally closed" mechanical timers?

John is right. Normally only heat type detectors are put in garages for
that very reason and because the typical fire in a garage will quickly
trigger the heat detector.

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math