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I have a newish room (built in 2008, New York), and the smoke alarm had a wiring setup I am confused about. It has 3 black wires, 3 white wires, and 1 red wire. See attached picture.

Anyone know why there are so many wires? Shouldn't alarms just need 1 black/white? Not sure what the red was for.

I would refer to the original alarm in there, but the owner told me they don't remember how it was setup when they took it down.

Related, there are two wall switches in the room that don't seem to control anything - I am now suspicious that they go to this box, but no idea why you would want 2 wall switches going to the same box that has a smoke alarm?

Thanks enter image description here

  • Any receptacles or light fixtures on the same circuit? That would explain the extra white/black. The red is used to interconnect the alarm signal of the smoke detectors, so if one sounds they all sound. – mmathis May 5 '17 at 19:56
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The red is probably the comm conductor for linked units. It is a bit odd that there's only one, but it could simply be the first in the chain. Without knowing the entire circuit layout I can't speculate further.

The extra blacks and whites are probably part of a lighting circuit on the same breaker. To connect your alarm you'd pigtail from each color.

Your mystery switches could be for switched outlets. Check for half-switched outlets where you'd expect end tables, for example.

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    Yeah, single red wire is the first or last alarm in the chain. The red isn't needed all the way to the breaker, just between all of the smoke alarms, so no need to pull the 14/3 any further. – mmathis May 5 '17 at 20:02

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