Check the model type on the back of the detector
If it is hardwired, turn off power at the circuit breaker first
Twist the detector counterclockwise to remove it from the mounting bracket
Open the battery compartment
Remove the old battery
Insert the new battery with the correct polarity
Close the battery compartment
Reattach the detector to the mounting bracket
Restore power if it was turned off
Press the test button to confirm proper operation
Replace the battery with the type specified by the manufacturer