The U.S. Federal Emergency Management Agency recommends changing smoke alarm batteries once a year. If you forget to do that and the battery runs down, most smoke alarms remind you with an intermittent, annoying chirping sound. Some smoke alarms take 9-volt batteries, while others take AA or AAA. Most smoke alarms need replacement after 10 years.
Look Up the Manual
Before changing the battery in your smoke detector, you need to know what kind of battery it takes and how to access the battery compartment. On some units, you have to remove the alarm from its mounting bracket to access the battery compartment, and it's good to know this before you start the procedure. It's usually easy to find the manual; navigate to the manufacturer's website and enter the model number for your unit into the search field. The model number usually is displayed clearly on the front cover. If you can't see it, look for the illustration that resembles your smoke alarm on the webpage.
Standard Battery Replacement
Most units don't require disassembly. You simply unlock the tab on the battery cover located on the front or side of the unit and pull to expose the battery. Pull out the old battery, install the new one and close the cover. If the battery is installed correctly, the cover should snap shut effortlessly. Push the "Test" button on the front of the unit to test the battery after replacing it; a piercing signal indicates the battery is properly installed. Some smoke alarms have sealed lithium batteries you can't replace. These units should be replaced -- battery and all -- every 10 years.
Disassembly May Be Required
Some hardwired units require disassembly before you can replace the backup battery. If yours is one of these, turn off the circuit breaker controlling the smoke-detector circuit, then press and hold the alarm's "Test" button for 10 seconds to discharge the system; the alarm may sound briefly. Separate the alarm unit from its mounting ring as required by your model: some units simply twist counterclockwise; others have a lock that you must depress before twisting. Disconnect the wire connector from the backside of the unit. Replace the battery in the unit as required. Reconnect the wire connector and lock the alarm unit back into the mounting ring. Press the "Test" button to make sure the battery is good, then turn on the circuit breaker.
Note: If your smoke alarms are connected to a security system, contact your monitoring provider for recommendations. You may need to place your system in "test" mode before replacing the batteries.
Ladder Safety Tips
Your ladder should be tall enough to allow you to work from the second-highest rung; standing on the highest rung is dangerous. Position all four legs of the ladder on solid, level ground, and get someone to hold the ladder if you have to climb higher than 8 feet to access an alarm on a vaulted ceiling. Don't bring anything up with you other than the new battery so you can use both hands for climbing.