Russ' Do It Yourself Home Workshop

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First Alert 9120B Smoke Detector Keeps Chirping/Beeping

Posted by Russell Wright on April 4, 2014

I had a smoke detector that kept chirping.  Thinking it was a battery problem, I replaced the battery even though the battery that was in it tested out okay.  Now, this is a smoke detector located at the top of the stairs, so I had to get my folding ladder out to get to it.  You know…two ladder feet on a stair and the other two feet of the ladder on the top of the stair landing with 6′-1", 210 lb. me standing on the ladder, reaching for the ceiling.  Not a pretty sight.  And, to make matters worse, the dang thing kept on beeping after I replaced the battery.


So, standing on the ladder (I didn’t put it away because I thought this might happen), I removed the smoke detector by rotating it CCW to detach it from its base so I could get to the plug on the back.  After unplugging it (and not falling off the ladder) I took it downstairs and removed the cover.  There are three plastic tabs/clips that can be released, one-at-a-time, to allow you to remove the cover.  I took the naked smoke detector out to the garage and fired up the air compressor (what…you don’t have one?) and blew the sensor clean.  I reassembled the detector (snapped it together) and put the original battery back in it and voila, no more chirping!

This detector is located near our attic fan, so I’m thinking it gets a lot of dust and particulate matter blown by it when the fan runs.  However, it looked very clean on the inside, but blowing it out appears to have done the trick.


10 Responses to “First Alert 9120B Smoke Detector Keeps Chirping/Beeping”

  1. Phillip Lane said

    We’re trying to find the 3 tabs that can be released to take the cover off. Help We don’t see them.

  2. Joe said

    One is located next to the battery release tab and the others are equally spaced apart from that one. Note three chirps every minute is a malfunction; not a battery issue. Unit most likely needs to be cleaned.

  3. said

    Mine was full of visible dust I opened the battery cover and blew into it the dust came out and it stopped chirping. Thanks Russell and Thanks Joe.

  4. Dudley said

    I have 2 brand new 9120Bs with brand new batteries. I reset them and they still chirp every 60 seconds. They are now going in the garbage can and they will be replaced with Kiddies next week.

  5. Ken DeLude said

    I have in the last two years approximately 3-4 cheap($5.00) First Alert (same model) smoke detector begin chirpings within months of purchase and batteries are good. I ended up throwing them away because I had disposed of my receipts . Just yesterday one I have had since 17 June 2017 began chirping and again the battery was good. Why has there not any public notice about this because I have just now found other complaints ab out the same problem/

    • Russell Wright said

      I have one or two of these that seem to get dirty faster than the others. One is near an attic fan. Probably exposed to lots of dust that gets in the sensor.

  6. Marcia said

    The chirping is in my bathroom where there is no smoke alarm. I have been trying to fix the alarm in the bedroom. This is the closest one to bathroom.
    This is on the 2nd floor, but there isn’t one downstairs below the bathroom. My system is wired. Please help if you can.

    Than you,

  7. NE said

    how do you remove the detector from the ceiling? It will not turn CCW

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