The Replacement Safety Sensors project an invisible light beam across the inside of the garage door to prevent accidents and are required for safe use of all Chamberlain Garage Door Openers. Whenever there is an obstruction, the garage door will automatically reverse before causing any damage. Chamberlain compatible, these sensors replace defective or damaged sensors for every Chamberlain Garage Door Opener manufactured after 1997. Easy setup and includes two sensors, mounting brackets, 18 in. of extension wire and instruction manual. Additional assurance with 1 year warranty.