My house has a wired smoke alarm system, three smoke detectors and one CO detector. These are all old firex detectors, I am replacing them with three kiddie smoke alarms where one is combo CO + smoke detector.

The problem is if I remove the old CO detector and leave it disconnected the alarms chirp every 5-10 minutes. I put it back in and the chirping reduced to rarely a couple times a day.

How can I fix this setup to remove that old detector from the system?

  • I have edited the title of your post to better match your actual question. Welcome to diy.stackexchange.
    – DoxyLover
    Commented Jul 7, 2020 at 10:07
  • 1
    All of your new alarms chirp, or just the one CO detector you have disconnected? Are these brand new detectors (can you check the manufacture date)? In my limited experience, occasional chirping has indicated a bad backup battery and the batteries are usually made to last for the useful life of the detector. Commented Jul 7, 2020 at 11:39
  • It sounds like there is an value in the detector needed for verification on some of the dumb systems I worked on years ago a simple 1k resistor was used to verify the sensor was not unplugged. With the smarter programmable systems they must be removed from the program map or disabled.
    – Ed Beal
    Commented Jul 7, 2020 at 13:11
  • @statueuphemism the only chirping one was the combo alarm. I had used the same wire order as the old firex, and just reinstalled it now and saw the white and black wires were wrong. I did this after it woke everyone up this morning with a false fire alarm. The CO detector is now disconnected and no issues. If no chirping in the next 24 hours I will update here as resolved.
    – jheagle
    Commented Jul 7, 2020 at 14:46

1 Answer 1


I solved this by re-inspecting the detector that was making the noise. I discover that the original wiring had reversed white and black power connections.

Perhaps the older alarms were not polarized.

I have no confirmed idea why the external CO detector impacted this system, my theory is it helped balance the load to offset the crossed wires.

After fixing the wiring, I was able to remove the external CO detector without any further issue.

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