Wireless Tri-Zone Door Window Sensor Features: Fully Supervised Wireless Transmitter Attractive Sleek Design (1.5'' W x 2.75'' H x 1'' D) Built-In Reed Switch and Tamper Built-In Tilt Switch Option (for securing garage doors without installing magnets) Easy Open Case for Battery Replacement LED Low Battery Indicator Tri-Zone Contact 319.5 MHz Crystal Version. Uses CR123A Lithium Battery. *The Secure Wireless Receiver (EV-REC3-ADM) is required for this device*