Ensure the green alarm indicator light is off and turn off the main electricity to the alarms on the property.Find the flattened T-shaped slot on the alarm's side; an arrow and sticker directing you there will state, "Insert screwdriver to remove."
Slide the alarm's head away from the screwdriver while you place a tiny flat-headed screwdriver into the slot. To detach the device, you should slightly twist away from the plate.
Then the old alarm will drop into your grasp.
Align the new unit with the mounting plate and slide it into place to attach the new alarm. When it's in position, you should hear a faint clicking sound.
Ensure the alarm's green indicator light is on and return the mains' power on.
Press the test button on the unit's front to test the alarm. An alert should sound from the device.