Driveway Patrol Sensor and Receiver Kit (Discontinued by Manufacturer)
When a visitor--wanted or unwanted--approaches a house on foot or in a  vehicle the motion-detecting sensor unit of this warning device sends a signal  to the receiver indoors, which chimes an alert. The device is wireless and has a  400-foot range. It requires three C-cell batteries for the receiver and one  9-volt battery for the transmitting sensor. (Batteries are not included.) The  sensor is housed in weather-resistant plastic, installs with a screw on any  surface, such as a mailbox post, garage, or door, and measures 4-1/4 inches  high, 2-5/8 inches wide, and 2-1/4 inches deep. The portable receiver has an  identical housing, can be set to chime high or low (or turned off), and measures  5 inches high, 3-5/8 inches wide, and 1-1/2 inches deep.--Fred Brack