How to Replace a Hardwire Smoke Detector

Written by steven douglas
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How to Replace a Hardwire Smoke Detector
Replacing a hardwire smoke detector isn't difficult. (sensor of broken window on ceiling image by StarJumper from

Smoke detectors provide a very important level of homeowner protection at a minimal cost. In many areas of the country, hardwire smoke detectors are mandated by building codes. Fortunately, replacing a hardwire smoke detector is no more difficult than replacing the batteries in a battery-operated smoke detector. In fact, most hardwire detectors also have a battery backup feature included in the design, so it is important for homeowners to become accustomed to both types of smoke detectors, and their maintenance.

Skill level:
Moderately Easy

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Things you need

  • 9-volt battery
  • Stepladder
  • Flashlight
  • Phillips screwdriver

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  1. 1

    Place a stepladder beneath the old hardwire smoke detector. Climb up and remove the plastic housing from the smoke detector. The plastic housing is usually held in place with two or three plastic tabs that must be pinched, or twisted.

  2. 2

    Turn off the electricity to the room or area that contains the hardwire smoke detector. Climb the stepladder again and, using a flashlight, locate the two mounting screws (usually Phillips screws) that hold the smoke detector to the electrical junction box in the ceiling. Remove these two screws.

  3. 3

    Pull the smoke detector down, until all the slack is gone from the three connecting wires (black, white and bare). Remove the wire nuts that hold the wires together by twisting each one counterclockwise. Pull the wires apart, remembering the colours of wires connected together (usually white attached to white, red to red, or black to black).

  4. 4

    Remove the old smoke detector, and attach the hanging wires from the junction box onto the new smoke detector, using the same colour coding as from the old smoke detector.

  5. 5

    Install the wire nuts by twisting them clockwise until tight. Reattach the new smoke detector to the ceiling gang box using new Phillips screws that came with the unit.

  6. 6

    Turn the power back on the circuit, and test the new smoke detector by pressing the red test button. If it beeps, install the plastic decorative cover.

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