I looked at this unit back in the Summer, wasn't impressed, don't recall why. I purchased a Miltronic electronic driveway alarm about six months ago. It works great. You have to purchase the transmitter and receiver. The transmitter uses a infrared beam to sense motion and transmits a signal 1000 feet to the receiver which has a beeper that sounds, not real loud. The transmitter is mounted on a tree 30 feet from the edge of the driveway about 100 feet from the house. The transmitter is 9volt battery operated. The receiver plugs into the house current. I also have two remote alarms that plug into wall outlets that are driven by the receiver. Not cheap, but works great, and senses everything that moves in the driveway area not just metal objects. Took about 20 minutes to mount and set up. There are a few tricks to getting this set up right. The transmitter must not face the sun, north is best, it should be no more than 24" off the ground tilted slightly down and use only regular DuraCell batteries, everything else loses their contact points internally as they wear out causing the transmitter to act funny. ric