How to Replace Hardwired Smoke Detectors

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You can replace a hardwired smoke detector.

The National Fire Protection Association advises that smoke alarms should be replaced every 10 years, and California, among other states, requires manufacturers to display the manufacture date on smoke alarms so that homeowners know when the 10-year period has elapsed. Even without this recommendation, savvy homeowners know that updating smoke alarms is a matter of safety as well as cosmetics, given that old smoke alarms get dingy and discolored, and painting them is not a code-compliant option.

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If you have battery-powered smoke alarms, the change is easy to make — just remove the old one and put a new one in its place. Hardwired smoke alarms require a bit more effort because they are wired into the home's electrical circuitry, so the job might call for a modicum of electrical wiring know-how unless the existing alarm has a pre-wired plug. Replacing a plug-in model, like the First Alert BRK 7010B or the Universal Security Instruments 1204, with an identical one is just as easy as replacing a battery model.

Things You'll Need

How to Replace a Hardwired Smoke Alarm

Step 1: Turn Off the Power

Locate the breaker in the main panel that controls the smoke detector circuit and turn it off. All the smoke alarms connected to the circuit may start chirping when you do this, and if it bothers you, don't worry. The job won't take long.

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Step 2: Remove the Alarm From the Mounting Ring

Climb on a stepladder that is tall enough to allow you to comfortably reach the smoke alarm. Grasp it with one hand and turn it counterclockwise a quarter turn to disengage it from the mounting plate. Pull it far enough away to see the wiring and if it's plugged in, pull out the plug.

Step 3: Test the Wires and Disconnect Them

If the smoke alarm isn't plugged in or you want to install a model with a different plug, you have to disconnect the wires. Pull the wire caps out of the electrical box and insert the probes from a voltage tester into the caps holding the black wires and the ground wires. If the light stays off, unscrew the wire caps and untwist the alarm wires from the circuit wires. You can now remove the alarm. Follow the same procedure to disconnect a plug that you want to replace with another one.

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Step 4: Replace the Mounting Plate (Optional)

Unscrew the mounting plate from the ceiling if you're replacing the alarm with a different model. Screw the new mounting plate to the ceiling, making sure the wires are centered in the middle of the ring.

Step 5: Wire the New Alarm or Plug

Twist the black hot wire on the new plug or alarm clockwise together with the circuit wires using pliers and then screw on a wire cap and tighten it. Repeat with the white neutral wires and the ground wires, which are either bare or green. Push the wires into the ceiling box. If you're replacing a plug-in model with a different type, you may be able to find a plug adapter that works, and that will save you from doing any wiring.

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Step 6: Install the New Smoke Alarm

Align the alarm with the notches on the mounting plate, push the alarm in as far as it will go and rotate it clockwise to lock it into place. You can now turn the power back on.

A Word About Batteries

Beginning in 2014, California law requires all smoke alarms to have sealed lithium-ion batteries, and many manufacturers have followed suit by making that type more available. You don't have to worry about installing batteries when you install a sealed smoke alarm. If you do select a model that requires a backup battery, don't recycle the battery from the old alarm. Install a fresh one.

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Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at Hunker and Family Handyman.