Locate the Alarm: Make sure you know where the alarm is mounted, whether on the ceiling or wall. Remove the Alarm: Twist the alarm counterclockwise to remove it from the mounting bracket. Open the Battery Compartment: Find the battery compartment on the back of the alarm. It usually has a hinged cover. Replace the Battery: Remove the old 9V battery and replace it with a new one. Ensure the positive and negative terminals are correctly aligned. Close the Battery Compartment: Snap the battery compartment cover back into place. Reattach the Alarm: Place the alarm back onto the mounting bracket and twist it clockwise to secure it. Test the Alarm: Press the test button to ensure the alarm is working properly.