How does the Safe-T-Beam reversing system work?
The Safe-T-Beam Non-Contact Reversing System uses an infrared beam that, when interrupted by an object, causes the garage door to automatically stop closing and reverse to the open position. Importantly, the door does not need to make physical contact with the object to trigger the reversal. (Page 2)
From the official Genie 2128 manual, page 2
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