The STKR Concepts Parking Sensor is designed to take the guess work out of parking your car in tight garage spaces. It features adjustable, ultrasonic range-finding technology. Simply mount the sensor unit in front of your vehicle at bumper level, then mount the signal light in a position easily viewed from the drivers seat. Lastly, park your vehicle exactly where you want it and press the set button. Thats it! Next time the driver approaches the Parking Sensor, they will see a green light indicating that it is safe to proceed, then a yellow light warning to slow down, and finally a red light when the chosen stopping point is reached. The STKR Parking Sensor eliminates the dents and dings from garage "fender benders" and allows you to safely close the garage door every time. Easy to install with the included double sided tape and Velcro, and adjustable between 1 and 4 feet. Powered by 4 AA batteries (not included).