Open the cover by loosening the small screw at the bottom of the sensor and expose the circuit board and remove the circuit board.
Locate the battery on the back side of the board and remove it. With the battery removed, press and hold the tamper spring. Reinsert the battery and immediately release the tamper spring and press and release the tamper spring again.
The green LED on the circuit board will begin to flash once defaulted to signal that the device is ready to add to your system.