Bosch Wireless Reed, Radion, RFDW-SMDual Reed Switches: Unlike many contacts, this unit has a reed switch on both sides, allowing you to place the magnet on either the left or right side for maximum flexibility. Detection Gap: The magnet must be mounted within 20 mm (0. 78 in) of the device. Tamper Protection: Includes both a cover tamper (if the lid is opened) and a wall tamper (if the unit is pulled off the frame). Battery Life: Rated for up to 5 years. Because it uses a standard AAA