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. Features: Compatible with Chamberlain, lift master and most craftsman For use with every Chamberlain garage door Use: replacement for damaged sensors Easy installation Enhanced trouble shooting, most intuitive safety reversing sensors Low profile reduces risk of being knocked out of alignment Whenever there is an obstruction, the garage door will automatically reverse 2-sensors, mounting brackets, 18 in. of extension wire, instruction manual Click here for more information on Electronic Recycling Programs