Original factory replacement infrared safety beams. The safety beam has two components, a sender and a receiver. The sender produces a narrow infrared beam that travels across the bottom of the garage door opening to the infrared receiver. If an object blocks the infrared beam while the garage door is closing, the garage door will stop, then reverse and fully open ( the opener's light will flash three times). As a safety feature, the garage door opener will ignore signals from all remote controls if the garage door is open and the infrared safety beam is blocked or out of alignment. In this case, the garage door can be forced closed by pressing and holding the wall station's up/down arrow pushbutton (be sure the garage door is in clear view). If the receiver's green LED is on, but the red LED is off, the receiver has power but is not detecting the infrared beam from sender. Check for: Dirt on the receiver's lens, Sunlight shining into the receiver's lens, A short in the safety beams wiring (from staples or at the garage door opener terminals), The safety beam is mis-aligned or something is blocking the beam.