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. It hangs on your garage wall and stops you precisely at a safe, pre-calculated distance from the wall. When you pull into the garage, you see the green light illuminate, then midway it changes to yellow, and when the light turns red youre 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..