It"s time to replace that tennis ball on a string with an Easy Park Garage Parking Sensor! The Easy Park Garage Parking Sensor will help you get into the garage and park perfectly every time. It has three lights and a distance sensor that can warn drivers when they are pulling in too close or not close enough. Think of it as a self guidance-system for parking your car. It hangs on your garage wall and stops you precisely at a safe, pre-calculated distance from the wall....every time. When you pull into the garage, you see the green light illuminate, then midway it changes to yellow, and when the light turns red you"re right where you want to be. Use the AC adapter (included) or you may also use 4 "AA" batteries if no AC outlet is available. Anyone who parks in a small or crowded garage will appreciate the accuracy the Easy Park system offers. No more crushed walls, lawnmowers or mangled golf clubs! With the Easy Park Garage Parking Sensor, you"ll never hit your garage wall again! Features: Built-in ultra sonic sensor knows your car"s bumper distance Automatically activates when car enters garage Includes AC adapter or battery powered and requires 4 "AA" batteries (not included) Simple to install and use On/Off switch Extendable coil cord that adjusts to various bumper heights Built-in screw insets for easy wall mounting All mounting hardware included