Installing Hard-Wired Smoke and CO Alarms

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Added protection comes with alarms connected to other detectors throughout your home

Installing Hard-Wired Smoke and CO Alarms

A hard-wired smoke or carbon monoxide (CO) alarm is wired to a 120V household electrical circuit and is connected to other detectors throughout your home. Hard-wired smoke and carbon monoxide alarms sound simultaneously, on all levels of your home, when a single unit detects smoke or gas. Units with battery backup provide extra protection by functioning even if a fire causes the power to go out.

While most local building codes require hard-wired smoke alarms in all new construction, there’s added security and protection if you’re installing one in an existing home, and the steps are the same whether you’re installing smoke alarms or CO alarms.

This guide gives you the steps to install a smoke alarm on walls. If you are not comfortable working with electricity, consider hiring a professional.

WHAT YOU NEED FOR THIS PROJECT

1
Cut holes for remodel boxes
Cut holes remodel boxes - Hard-Wired Smoke CO Alarms

• Identify where the smoke alarm will be installed.
• Use a stud finder to determine the location of wall studs around each alarm location. Mark a spot for each alarm in the open space between studs on the wall 12-inches down from the ceiling.
• Use a marking tool to trace the outline of the remodel box on the wall. Use a level to make sure the box outline is straight.
• Drill a ½-inch starter hole at the corner of your outline.
• Starting at the hole, cut along the outline with your drywall saw.
• Test the fit remodel box. It should fit into the hole snuggly, but not so lightly that you have to force it. Do not set the remodel box yet.
• Repeat this process at each location where an alarm will be installed.

2
Run cable to the first alarm
Run cable first alarm - Hard-Wired Smoke CO Alarms

• See our Running Electrical Wire Behind Walls project guide for step-by-step instructions on how to run wires behind walls.
• Run Romex 14-2 NM-B cable from the breaker panel to the location of the smoke alarm closest to the breaker panel. Do not connect the cable to the breaker panel yet. You’ll do this at the end of the project.
• When the cable reaches the alarm location, pull about 10 inches of the cable through the knockout of the first remodel box.

3
Install next runs of wiring
Install next runs  wiring - Hard-Wired Smoke CO Alarms

• Run Romex 14-3 NM-B cable from the first alarm to the second alarm, leaving 10 inches of cable hanging out of the work box. Unscrew the faceplate from the starter outlet.
• Run Romex 14-3 NMB-B wire from the second box to the third, from the third to the fourth and so on until you reach the last alarm.

4
Secure the cable and set the box
Secure cable and set the box - Hard-Wired Smoke CO Alarms

• At the last alarm, pull roughly 10 inches of the cable through the knockout of the remodel box.
• Secure the cable in the box by tightening the wire clamp in the box.
• Set the box in place.
• See our Installing Remodeling Boxes project guide for detailed instructions.

5
Strip the wires
Strip the wires - Hard-Wired Smoke CO Alarms

• Still working at the last remodel box, use wire strippers to cut the NM-B cable’s outside sheath and any paper insulator to expose the black, white, red and bare copper wires within.
• Attach the copper wire to the box with a ground screw.
• Use wire strippers to strip ¾ inch of insulation from the ends of the wires.

6
Wire the alarm
Wire the alarm - Hard-Wired Smoke CO Alarms

• The alarm has two parts: the alarm itself and the harness with wires coming out of it that plug into the alarm after the wires have been connected. Use the harness with black, white and red wire for the following steps. Do not attach the plug to the alarm yet.
• Connect the black wire coming out of the box to the black wire on the harness and secure the wires together with a wire connector.
• Connect the white wire to the white wire on the harness in the same way.
• Connect the two bare copper ground wires together and connect them to the remodeling box.
• Connect the red wire from the harness to the red wire coming out of the box.
• Secure all wiring with wire connectors.
• Wrap electrical tape around the base of each wire connector.

7
Attach mounting plate
Attach mounting plate - Hard-Wired Smoke CO Alarms

• Place the alarm’s mounting plate on the remodel box and align the screw holes. Make sure the wire connection runs through the mounting plate.
• Carefully put the connected wires and plug through the mounting plate.
• Connect the wired harness to the back of the smoke alarm. These are usually configured to ensure they can only fit one way.
• Use appropriate sized screws to connect the mounting plate to the remodel box.

8
Attach alarm to the base
Attach alarm to the base - Hard-Wired Smoke CO Alarms

• Line up the notches on the back of the alarm with those on the base.
• Twist the alarm until it locks into place.
• Check the connection to ensure it is secure on all sides.

9
Connect and mount remaining alarms
Connect mount remaining alarms - Hard-Wired Smoke CO Alarms

• Continuing to work back toward the alarm closest to the breaker panel, repeat the actions in Steps 4 and 5.
• At each location, connect the black wire on the harness to the two wires coming out of the box. Connect the white wire on the harness to the red wire coming out of the box. Connect the red wire on the harness to the red wire coming from the box.
• Secure all wiring with wire connectors.
• Wrap electrical tape around the base of each wire connector.
• Connect the harness to the smoke alarm.
• When you reach the alarm closest to the breaker panel, connect the black wires, the white wires and the red wires.
• Mount each alarm as detailed in Steps 7-9.

10
Connect at the breaker panel
Connect at breaker panel - Hard-Wired Smoke CO Alarms

Connect the 14-2 NM-B cable to the beaker panel following the step-by-step instructions in our Adding a New Circuit project guide.

11
Test the alarms
Test the alarms - Hard-Wired Smoke CO Alarms

• Turn on the power to the circuit.
• Confirm each alarm’s power light is on.
• Press the test button on each alarm. You should be able to hear all the alarms each test.
• If the alarms don’t sound, turn off the power at the breaker panel and double-check your wiring connections. If the connections are correct but a unit’s power light won’t come on, replace the unit.

12
Install backup batteries
Install backup batteries  - Hard-Wired Smoke CO Alarms

• When you have confirmed all alarms are operating correctly, open the battery compartment cover on each alarm.
• Install a battery, being careful to position it so positive contact meets positive contact and negative contact meets negative.
• Close the battery compartment.