The Safety Technology International 34101 Sensor for Solar Driveway Monitor is to be used with the Solar Powered Wireless Driveway Monitor or Battery Powered Wireless Driveway Monitor. It uses a patented magnetometer sensor system. Movement of any large metallic (iron or steel) object having a magnetic field will cause the sensor to transmit to the receiver.
Under ideal conditions, the sensor may be placed as far as 1000 feet away from the receiver in your home. For best performance, place the sensor within 500 feet of the receiver.