The Ecolink TX-E251 Long Range Door/Window Sensor Qolsys, GE & Interlogix Compatible with Extended Battery Life DWS is a sensor intended for installation on doors, windows, and other objects that open and close. The sensor transmits signals to the control panel when a magnet mounted near the sensor is moved away from or closer to the sensor. The TX-E251 features a high capacity CR2 lithium battery for extended battery life, and maximum performance output power for long range applications. The sensor features two separate zones: zone 1 can be used for either of the two reed switches, and zone 2 can be used as an external contact option. The sensor is also equipped with a cover tamper switch for additional security.