How to change a battery in a fire alarm

If you are like many homeowners, you pay little attention to your smoke detector's battery. You installed the smoke detector, pressed the test button once, then forgot about it until it started chirping at you as a battery replacement reminder some months later.

How to Replace Most Smoke Detector Batteries
Smoke detectors' battery replacement operations vary, but there are some common features:
You will need to access the smoke detector with a ladder or chair as most are ceiling-mounted (though a few may be mounted high on a wall).
Most smoke detectors must be removed from the ceiling to replace the battery, though some do have a front-loading door. Twist the detector counterclockwise. The smoke detector should be released, with the mounting plate remaining on the ceiling. Some smoke detectors will have a tamper-resistant feature to prevent children from removing the device. Disengage with the locking pin.

Replace the battery as directed by the smoke detector instructions
Place the smoke detector back in the mounting bracket and slightly twist clockwise. The smoke detector should engage.
Test the smoke detector with the testing button usually located on the face of the unit.

How to Replace a Smoke Detector Hardwired With a Backup Battery
This type of smoke detector receives Electrical Wiring, Circuitry, and Safety as its main power source and has an onboard battery that is used as a backup in the event of power failure. At your home's Electrical Panels: Replacement Signs, Maintenance, and Homeowner Basics turn off the household power to the circuit supplying the smoke detector by switching off the proper circuit breaker.

Use a ladder or chair to access the smoke detector
Remove the smoke detector from the mounting base by turning the smoke detector counterclockwise. If the smoke detector does not disengage, it may be because of a tamper-resistant mounting bracket. Disengage by pushing the locking pin into the unit. Alternately, in some units, the pin is pulled out from between the base and the detector.
Do not immediately try to pull off the smoke detector as it is connected with a wiring harness. Tilt the smoke detector to the side and locate the wire connector leading into the unit. Unplug the wire from the smoke detector or mounting base, as applicable. Replace the smoke detector's battery at the door usually located either on the side or the back of the unit.
Reconnect the wiring harness to the unit or base, fit the unit onto the base, and turn the unit clockwise to engage it on the base. Turn on the circuit breaker to restore household power to the detector's circuit.

Test the smoke detector with the test button
10-year sealed lithium-ion smoke detectors' batteries are never replaced. Instead, dispose of the entire unit responsibly and replace it with a new unit. All smoke detectors should be replaced every 10 years or so, anyway: The manufacture date will be stamped on the back of each unit, so you know when it needs to be replaced.