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Question DetailsAsked on 8/23/2017

Our hard wired smoke alarm is not connected to any other smoke alarms. Can I tuck the red wire into the ceiling?

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1 Answer


That is the interconnect alarm wire - connects to other similar design/voltage alarms so when one alarm unit sounds, all the intercoennected alarms sound also. Makes it tough to tell which is causing the alarm if your model does not have an ALARM LED to show which is activated (if cause is not obvious) but largely eliminates the risk that an alarm in a room not currently occupied will not be heard. Especially at night - one of the interconnected alarms should be in bedroom hall outside master bedroom so it will hopefully wake people if any of the interconnected alarms (commonly put in child's room, kitchen, and utility/furnace room at minimum) goes off.

Since yours is not connected to other alarms, that red wire serves no function in your case.

HOWEVER - when the alarm self-tests (in some brands), when it alarms, and in some or most brands when it starts chirping because of a low battery, that wire WILL carry voltage. So - not only could sticking it up in the ceiling possibly cause a false reading during the self-check routine, but if the bare end contacts anything the least conductive or wet (which can include nails, fiberglass insulation, damp insulation, damp wood, etc), it could possibly discharge the alarm battery. Plus, with some model (mostly commercial ones without batteries) that is a 110/120V wire, not the 9V most household alarms have - so in that case a significant safety and fire hazard to just stick it up there.

Proper treatment is to use a small-gauge wire connector which will twist tightly onto it by itself (or regular household wire size by doubling the end over on itself), electrical taped on to be sure it does not come loose if you are safety obsessive like me, then curl the wire up and stash at the back of the alarm (behind the back plate in some models, between alarm and base plate in ones with lots of space). I prefer curling it up in the space between backplate and alarm, so if the alarm is removed an electrican can see the red wire is terminated there, otherwise it looks like it is going through the backplate to an interconnected alarm and someone might waste a bunch of time trying to find the one(s) it is interconnected with.

Sounds like you know what the red wire does - but if any doubts or if you ever have problems with interconnected alarms giving flase alarms, here are links to a few related previous questions with answers:

Answered 3 years ago by LCD

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