Trip the circuit breaker at the fuse box to discontinue electric power to the room where the fire alarm is mounted. Place a ladder beneath the fire alarm, if it is mounted to the ceiling, or next to the wall where the alarm is located. Twist the cover off the alarm and set it aside. Remove the battery from the battery compartment, unless there is no battery.
Remove the screws from around the alarm, using a Phillips screwdriver. Place the screws in your pocket to keep them from getting lost.
Pull the alarm away from the wall plate to which it was mounted. Stretch the wiring that is attached to the back of the alarm.
Take a picture with a digital camera of the wires from the alarm that are attached to the wires from the hole.
Check the picture on the camera's LCD screen against the diagram from the instruction manual that came with the alarm to confirm that the wires are correctly connected. Regardless of whether or not the wires are connected correctly, proceed to twist off the screw-tab connectors from over the twisted pairs of wires.
Place the connectors in your pocket. Separate the wires from the alarm and from the hole from each other. Scrape the exposed ends of the wires from the hole and from the alarm with the blade of a utility knife. Stop scraping a wire when the copper of the exposed end is shiny.
Shake a can of electrical cleaning spray for five seconds. Spray a one-second burst on the end of each wire.
Twist the wires from the alarm and from the hole around each other in the manner noted in the instruction manual that accompanies the alarm; if the wires were correctly wired prior to being sprayed, use the picture on the camera as your reference for wiring.
Screw a screw-tab connector over each pair of twisted wires. Push the wires into the hole. Press the alarm against the mounting plate and reattach the screws. Place the battery back in the battery compartment, if there is one. Twist the cover back on the alarm. Restore the electric power at the fuse box. Press the “Test/Reset” button on the side of the alarm for a second to reset the alarm. Put the ladder away.