These are being used to prevent theft of autos, provide increase security in buildings, to operate electronic gates, garage doors, computers,etc. Consists of a small key fob that is totally self contained (no moving parts or batteries) and a proximity sensor and associated receiver circuit box. When the key fob is brought within 3 inches of the sensor, the unique date incoded in the key fob is transfered to the sensor-receiver, activating whatever device-relay, solenoid, light, locks, etc.- that you have connected to the receiver. These are brand new units consisting of two key fobs, a master programer key in a sealed container, and a receiver box with sensor. The receiver is very sophisticated and can not be activated except by the key fobs that come with it. If someone steals one of the key fobs, you may program a new code with the master programer key fob into a remaining fob so that the stolen one will no longer work. The coding of new keys does not use a compute and can easily be completed in a few second period. The system is absolutely amazing. The reciever operates on 12 VDC Details: The key fob is completely waterproof, and crunch resistant. Size:l.4" square and is meant to be attached to your keychain and has a recessed circle to allow you to place a custom label (if desired). The sensor is about 2.1" x 1.3" and is attached by 20" cable to the 4 1/8" x 2 1/8" receiver box. The sensor can be mounted in wood, behind glass or plastic and still function perfectly. The sophisticated receiver uses 6 ICs and have 12V OUT PUT WHEN TRRIGER . when the correct key fob is brought within 3 inches of the sensor. THE UNIT PUTS OUT 12V OUT PUT (MUST BE WIRED TO 12V REALAY), and when key removed from sensor relay will open.This new technology has thousands of applications. As soon as you buy one of these units you'll want to purchase more as you realize all the different ways it can automate or control security tasks. Brand new with complete instructions,UNIT WILL COME WITH COMPLET WIRING DIAGRAM.