autonut843 wrote:
Hi,
I have noticed in newer homes that they have smoke detectors that take
both a battery and are plugged in to the AC. I think the wires running
between them seem to have an additional conductor and if one smoke
detector goes off and starts beeping, shortly thereafter, the other
ones start beeping as well. How does this work? If you were to mix
and match between different smoke detector vendors (all having the
interconnect feature, of course), would they all work the same? Is
this an industry standard connection? I assume it is an additional
conductor that either gets shorted to ground or hot by the tripped
smoke detector and when the other ones detect that short to ground/hot,
they start beeping as well.

Does any company make something that could tap in to that extra wire so
that, say, if I wanted to turn on emergency lighting or something like
that, it could trip a relay to do that? I'm thinking something that
wires in like a door bell transformer where the line voltage AC is all
in the box and the relay contact screws are outside where they belong,
not sharing a box with the line voltage at all.

Of course, if company XYZcorp makes an "interconnect smoke detector
relay module" that is UL etc approved and can be legally connected to
the smoke detector wiring harness in a standard single gang box and
will trip a NO/NC relay when the detectors are beeping, I'd like to
know about that.

Since IMO, smoke detectors are life safety, I'm not thinking about
modifying anything or experimenting on my own. It is more just a
curiosity on how the thing works and if there is an industry standard
or not. I am sure some of you have modified smoke detectors to do
something like this, but I would prefer if these mods were kept out of
this thread since I think there are many that feel this is no problem
and there are many that feel that modifying a smoke detector is a
dangerous thing to do. I, personally, would rather not be lead away in
handcuffs after explaining to the fire investigator the cool mod I did
to my smoke detectors that caused them not to work when I needed them
most and, golly, I don't see why it didn't work right, should I get a
lawyer now? the circuit really should have worked....

Thanks

You would think that they would make an industry standard for that sort
of thing, but unfortunately, not only is there no industry standard,
the interconnect specs are different between different smoke detector
models from the same manufacturer. There are low voltage
interconnects, and line voltage interconnects. And ther eare different
standards for the low voltage interconnects. I wired up 9 smoke alarms
with interconnects in our house, went and bought 1 hardwired detector
w/ battery backup for each floor of the house, and the remaining ones
were hardwired models without battery backup. (I figured that one
battery backup per floor was sufficient.) Well, after installing
everything and testing it, I discovered that the battery backup ones
will only remotely sound the other battery backup ones, and the
no-battery-backup ones will sound other no-battery-backup ones. After
reading the fine print buried in the instructions, it does in fact say
that you have to have the exact same model for the interconnect to
work. Oh well. I assume that there is some modulated signal that is
sent over the interconnect line as opposed to a simple high/low voltage
to signal the other units, although this is just speculation on my
part, and I've never tested it out. (I'd have to borrow an
oscilloscope from work if I wanted to try out that theory.)

Ken