What do the red and green lights on garage door sensors mean?

The red and green lights on garage door sensors are diagnostic indicators that tell you the status of the safety system, and their meaning depends on whether the light is solid or blinking and which sensor it is on. On Genie and Overhead Door systems that use red and green, a solid red light on one sensor typically means the sending sensor is powered and emitting the infrared beam correctly. A solid green light on the opposite sensor means the receiving sensor is powered, aligned, and successfully receiving that beam, so the system is safe and the door can close. If the green light is blinking, it means the receiving sensor is not aligned, the beam is blocked, the lens is dirty, or sunlight is interfering. If the red light is blinking, it indicates a wiring fault, no power, or a failed sending sensor. If both lights are off, there is no power from the opener. On LiftMaster and Chamberlain systems, you will normally see yellow and green rather than red and green, but the logic is the same. Yellow equals sender with power, green equals receiver aligned. Any blinking light means the door will not close automatically as a safety precaution and you need to clean, realign, or check wiring.