How to Hard-Wire Fire Alarms

Place the fire alarm face down on a work surface. Strip 1/2 inch of insulation off each wire attached to the back, using wire strippers. If there are no wires attached to the back, strip the wires attached to the wire plug clip instead, and then insert the clip into the slot on the bottom of the alarm.

Go to your home's fuse box. Trip the circuit breaker that supplies power to the area --- for example, a living room or bedroom --- where the fire alarm is going to be installed.

Place a plastic tarp against the wall where there is an AC outlet. Place a ladder against the wall. Draw an imaginary line straight up the wall from the AC outlet. Cut a small hole with a utility knife just below the ceiling at the top of the wall along this imaginary line.

Shine a flashlight into the hole to find the electrical junction box inside. Cut a larger hole, using a drywall handsaw, so you can access the electrical junction box. Dispose of the cut wall section in the trash.

Place the fire alarm's mounting plate on the wall, over the hole. Attach the plate to the wall, using wood screws and a Phillips screwdriver.

Loosen the screws on the electrical junction box in the wall, using the Phillips screwdriver. Wind the end of the black wire from the fire alarm around the screw on the electrical junction box that already has a black wire wound around it. Wind the end of the white wire from the fire alarm around the screw on the electrical junction box that already has a white wire wound around it.

Loosen the screw at the bottom left or right of the electrical junction box, using the Phillips screwdriver. Wind the end of the remaining wire from the fire alarm around this screw. Tighten all of the screws.

Push the wires into the hole. Place the fire alarm against the mounting plate. Twist the fire alarm onto the mounting plate with a clockwise motion. Take the ladder away. Remove the tarp. Restore the electric power at the fuse box.