Get the correct replacement battery for your First Alert smoke alarm
Twist or slide the alarm off its mounting bracket, if needed
Open the battery compartment
Remove the old battery
Insert the new battery with the correct polarity
Close the battery compartment
Reattach the alarm to the mounting bracket
Press and hold the test button to confirm it works
Replace the battery immediately if the low-battery chirp continues
Replace the entire alarm if it is hardwired with a sealed backup battery or if it has reached its replacement date