Keep track of the comings and goings on your property with this motion-activated alert system. When a vehicle or person passes the sensor, the receiver emits an audible tone and lets you know someone's there. Use it to monitor the mailbox, the driveway, the garage or the front door. Battery power and 400-foot range means no wiring is necessary. Operates on three C-cell batteries or one 9-volt battery; both are included.