Short version:

I would like to hang smoke detectors with 10-year lithium batteries over the junction boxes that were once used for a wired system. The wires in the boxes no longer carry any current. What else do I need to do to protect the new alarms (other than double-checking that the wires in the junction boxes aren't live)?

Long Version:

In 2018, I replaced our old and failing wired system with a set of First Alert P1210 detectors with "10-year" lithium ion batteries. The batteries on these alarms keep failing after 18 to 24 months (1). (I'm now on my 3rd set.)

When replacing them this time, First Alert Customer Service asked if they were installed over an old wired system because doing so could lead to premature failure. They are, but the current to the old system was turned off before I put the new alarms in back in 2018. (I even checked with a current tester to make sure the wires weren't live.) Do I need to do anything else to correctly put the First Alert alarms over top of the old junction boxes? (I'd rather not have to patch the drywall only to hang a smoke alarm somewhere else.)

Or, since there has never been any current in the junction boxes, is there another issue I should be looking for?

Or, do I just need to keep getting them replaced until the 10-year warranty is up then try a different brand?

(1) To be specific, the low battery chirp is starting between 18 and 24 months. I suppose there is a small chance the problem is the circuit that detects the battery level.

  • 1
    The only thing I can think of is the boxes are somehow holding heat in and damaging the electronics/batteries. Not enough ventilation. Or you got defective product.
    – crip659
    Commented Jun 24, 2022 at 16:07
  • 1
    Did First Alert customer service tell you that if P1210 is "installed over an old wired system" it will fail prematurely? That is not clearly stated in your narrative.
    – MTA
    Commented Jun 24, 2022 at 17:47
  • just make sure to seal up the dead box with foam or tape or insulation; any "stuff" to kill leaky drafts so it doesn't draw smoke to itself.
    – dandavis
    Commented Jun 24, 2022 at 20:47
  • "hang smoke detectors with 10-year lithium batteries over the junction boxes" - absolutely not. Permanently covering a junction box violates code, to keep everything from being a giant mystery when you call in an electrician, which is what your plan will do. Blank cover plates. Place detectors elsewhere. Whether two screws into a plastic ring is permanent, IDC. "You could probably plaster over the junction box, if the wiring inside has been thoroughly decommissioned." You could. I could also strangle you.
    – Mazura
    Commented Jun 25, 2022 at 23:22

1 Answer 1


According to their website battery smoke detectors are not meant to be installed over junction boxes because it can cause nuisance alarms. Which makes marginally more sense, though still very little, than saying they will fail prematurely.

Still, the objection seems to be related to the box, and probably air flow through the new detector, rather than to the wires inside.

The smoke detector is tested and certified for installation on a wall or ceiling, so they want you to install it that way. For something that is supposed to save your life and needs to function properly either zero or one times in ten years, I think you should follow the instructions no matter how much they are annoying or don't make sense.

You could probably plaster over the junction box, if the wiring inside has been thoroughly decommissioned.

  • OP doesn't have a false alarm problem though, it's an early-failure problem. The reason an opening behind the detector can cause nuisance alarms is that it allows a constant and more concentrated stream of, say bacon smoke, to hang out in and around the detector compared to it sitting in a air-flow dead zone and just catching a side-waft. Detectors usually ignore minor particulate concentrations as presumed nuisances, so a small increase can push the detector "over the waterfall". That said, nuisance alarms do run down batteries as the buzzer uses FAR more power than just monitoring.
    – dandavis
    Commented Jun 24, 2022 at 20:42
  • @dandavis to be fair, I failed to address why OP's devices "keep failing" at less than 20% expected lifespan. I just provided whatever factual info I could find. I really can't fathom why multiple detectors would actually fail after 18 months, unless they are in fact filling up with airborne bacon particles.
    – jay613
    Commented Jun 24, 2022 at 20:53
  • answer's good info for searchers and has an official source addressing the topic. you're that right there's not a good reason for the failure, perhaps bad luck, shipping delays, corroding offgasses, etc.
    – dandavis
    Commented Jun 24, 2022 at 21:02
  • If it's a problem of the box's additional air passage then one option may be to install a box cover plate while installing the alarm - just slip it above the alarm and utilize the same screws you're using with the alarm. If the remaining small air gaps are still a problem then just caulk the cover plate up there to seal it. Then install the alarm. Commented Jan 13 at 13:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.