Replacing an AC-powered smoke detector.

Electrical Repairs:

Replacing An AC-Powered Smoke Detector

In This Article:

The power is turned off, the old smoke detector is removed, and the wires are disconnected. New wires are connected and the new smoke detector is installed.

Related Articles:
Skill Level: 2 (Basic) Time Taken: About 30 Minutes

By , Editor


There are a couple of reasons why you might need to replace a smoke detector:

  • Maybe the existing detector is too sensitive and squawks whenever you're using the oven.

  • Maybe you don't like the appearance or the sound of the old one.

  • Perhaps you want to upgrade to a dual function detector, which employs both ionization and photoelectric sensing techniques.

  • Manufacturers of smoke detectors say to replace the unit after 10 years of use.

  • Sometimes smoke detectors just malfunction. I know two families who have had AC-powered interconnected smoke detectors suddenly start screeching for no reason at all. In both cases this false alarm happened in the middle of the night, and the homeowners had to figure out which smoke detector was faulty and unplug it, not a simple process in a big house when you've been woken from a deep sleep.


When Inter-Connected Smoke Detectors Sound A False Alarm:

If you are certain that the smoke detectors are sounding a false alarm, and the hush feature fails to silence the beeping, then it's necessary to remove and unplug smoke detectors one-by-one until the beeping stops. (The last unit unplugged would be the faulty one, of course.) The other detectors could be re-installed, and the faulty unit should be replaced as soon as possible.

Alternatively, you could just turn off the circuit that powers the smoke detectors. While some "safety experts" may bristle at the suggestion of going even one night without working smoke detectors, I'll point out that until smoke detectors were introduced in the late 1970's, everyone did that every night.

But here's a problem: In lots of houses I've seen, it's not easy to locate the breaker that supplies power to the smoke detectors. Consequently, I have used a permanent marker to write "Smoke Detectors" or "S.D." on the breaker panel cover, with an arrow pointing to the breaker. That makes it easy for the homeowner to find the offending circuit in the middle of the night, in the event of a false alarm.

In my own house, I have a couple of plain-old battery-powered smoke detectors in addition to the interconnected AC-powered units.


Most smoke detectors simply twist off the base plate. Usually the smoke detectors needs to be turned counter-clockwise to remove it.


If there are no wires behind the smoke detector when it's removed, it's a battery-powered unit.

Removing smoke detector by twisting counter-clockwise.


Editor's Note: I created this brief article to explain the procedure for replacing an existing AC-powered smoke detector. While these pictures are taken from my article about installing new smoke detectors with new wiring, they should help explain the procedure.


Smoke detector removed from base, showing 3-wire pigtail supplying power to detector. Then the electrical connector to the smoke detector can be unplugged.

Be careful... the plug may have plastic "catches" that need to be pushed, pulled or squeezed to release the connector.


Then the mounting plate (base plate) can be removed. Removing smoke detector base plate from electrical box.


Typical smoke detector wiring, showing detector pigtail and 14-3G house wiring. The wires can be pulled out of the box.

The twist-on electrical connectors (wire nuts) would be removed next. Those are the little yellow caps in this photo.

(At this step you REALLY want the power to be off.)


Then the ends of the wire can be untwisted with pliers and the smoke detector pigtail can be removed. Twisting or untwisting wires with pliers.


Stripping extra insulation from stranded wires. I like to strip a little more wire from the ends of the pigtails. With stranded wire, I prefer about 3/4 inch of bare wire at the end, so it can wrap around the solid wire.


Then the new pigtail can be connected to the house wiring, and the wires can be tucked into the junction box.

Then the base plate can be installed, the smoke detector plugged in, and secured to the base. Turn the power back on and test the new smoke detector.

Wires tucked into electrical junction box, leaving smoke detector pigtail sticking out.


Hush Feature:

Most newer smoke detectors have a "hush" button, which you push and hold until the beeping stops. On some smoke detectors you simply press and hold the test button to hush the device. When hushed, usually the device will ignore any detected smoke for 15 minutes, and then it will be "on guard" again.

More Info:

Tools Used:
  • Phillips Screwdriver
  • Wire Strippers
  • Lineman's Pliers
Materials Used:
  • Smoke Detector, AC-Powered
  • Twist-On Electrical Connectors (Wire Nuts)
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Written February 15, 2010