Garage Door System GuideThe two small sensors near the bottom of a garage door track are the door's entrapment protection. CPSC notes that an external entrapment protection system, which can be an electric eye, was added to the federal requirement in 1993, and that an electric eye should be installed at a height of 4 to 6 inches above the floor. When the beam between the sensors is clear, a solid green LED confirms alignment; when it is broken, the LED blinks and the opener refuses to close. The sections below explain how to read the lights and re-aim the receiving sensor.
What the safety sensors do
The sensors exist because a closing door is a crushing hazard. CPSC records that all garage door openers manufactured or imported for sale in the United States after January 1, 1991 have reversing systems, and that a requirement for an external entrapment protection system was added in 1993.
That protection can take the form of an electric eye, a door edge sensor, or another device that provides equivalent protection. CPSC specifies that if an electric eye is used, it should be installed at a height of 4 to 6 inches above the floor, low enough to catch a child or pet in the door's path.
Read the LED indicators
Alignment shows itself in the indicator lights before you touch anything. The Chamberlain and LiftMaster support guidance states that when both LEDs are on solid, the sensors are aligned and functioning properly.
A changed light points straight to the fault. The same guidance explains that a blinking green LED means the sensors are misaligned or obstructed, and that if the sending sensor glows steadily while the receiving sensor is off or flickering, the cause is typically a misaligned or obstructed sensor. Reading the lights first tells you whether to re-aim the receiving sensor or hunt for something breaking the beam.
Align the receiving sensor
Only the receiving sensor, the one with the green LED, needs aiming. The Chamberlain and LiftMaster guidance directs you to loosen the wing nut on the receiving sensor and point both lenses directly at each other.
The green light confirms the fix. The guidance says to tighten the wing nut once the green LED glows steadily, and to confirm both LEDs are solid, which means the sensors are aligned. Tightening the wing nut without shifting the sensor is what keeps the beam locked in after you let go.
When the LED stays off
If aiming does not restore a steady light, the beam is not the problem. The troubleshooting guidance notes that the safety reversing sensors must be connected and aligned correctly before the garage door opener will move in the down direction, so a dead LED usually points to wiring or a failed sensor.
The guidance walks through the wiring check, confirming that the white wires connect to the white terminals and the striped wires to the black terminals. If the sensors test dead at the opener even after the wiring is verified, the fault has moved past alignment and into part replacement.
Confirm with the reversal test
Aligned sensors still need a function test to prove the door reverses on contact. CPSC describes placing a 2x4 on the floor of the garage in the door's path, and notes that if the door does not properly reverse when striking the 2x4, the opener should be disengaged until it is adjusted, repaired, or replaced.
Make the check part of a routine. CPSC advises inspecting the garage door and the garage door opener every 30 days, which keeps both the beam alignment and the reversal response verified rather than assumed.
Frequently asked questions
How high should garage door safety sensors be mounted?
CPSC specifies that an electric eye should be installed at a height of 4 to 6 inches above the floor, low enough to catch a child or pet in the door's path.
What do the sensor LED lights mean?
Per Chamberlain and LiftMaster guidance, both LEDs on solid means the sensors are aligned and working. A blinking green LED means the sensors are misaligned or obstructed.
How do I realign garage door sensors?
Only the receiving sensor with the green LED needs aiming. Loosen its wing nut, point both lenses directly at each other, and tighten the wing nut once the green LED glows steadily and both LEDs are solid.
The LED stays off after aiming. What now?
A dead LED usually points to wiring or a failed sensor rather than alignment. Check that white wires connect to white terminals and striped wires to black terminals; if the sensors still test dead, the part likely needs replacement.