Check the smoke alarm type and battery compartment
Turn off power to the alarm if it is hardwired
Remove the alarm from 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 if it was removed
Restore power if it was hardwired
Press the test button to confirm it works
Replace the battery immediately if the low-battery chirp continues