The red light on the receiving sensor glows bright red when the sensors are aligned properly. There usually is a light on each sensor. Hi. If one or both of the green/red and yellow/orange lights do not turn on, replace the safety eyes; they are defective. The units are placed near the ground on either side of the garage door. Linear garage door openers have a green light on the sending sensor and a green and red light on the receiving sensor. If the beam of light is interrupted while the garage door is closing the door will stop and rise back up. I moved the red one and the red light stopped blinking but the door still won't open. This morning Garage door sensors utilize a photo-eye sensor and a beam of infrared light that goes between the two units. Contractor's Assistant: I'll do all I can to help. The green lights let you know there is power going to the sensors. One will have a green light that signifies power to the units, and the other will have a red light that signifies that the sensors are `seeing' each other (i.e. Do Both Garage Sensors Need to Be Green? If it does, the sensors are okay, and there’s a fault with the wiring somewhere. One sensor is red and one is green. The sensors are little black boxes about the size of a deck of cards that can be found on either side of the bottom of the garage door. How long have you been dealing with this? I put a new battery in the remote too. My genie garage door won't open . However, if both lights do turn on, operate the garage door with its automatic opener as normal to ensure that the door closes as it should.