# Garage Door Safety Sensors: Height, Alignment & the Monthly Test

> Garage door photo eyes must emit a beam no higher than six inches above the floor and sit within six inches of the door path. DASMA asks for two tests every month. Here is how to do both, and what a blinking sensor means.

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- Page updated: 2026-08-31

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The two small eyes near the floor are the reason a garage door reverses instead of closing on a child. There is a published rule for how high they sit and how far apart they go, and there are two tests the industry asks every homeowner to run once a month. Both take under a minute.

By Garage Doorman, Grimsby, Ontario · Updated 31 Aug 2026

**6 inches**: Maximum height of the photoelectric beam above the garage floor.

**Within 6 inches**: How close the sensors must sit to the path of the door.

**Every month**: How often DASMA asks you to test both the photo eyes and the reversing mechanism.

## What the sensors are, and what the law of the product is

Residential garage door operators labelled and listed to ANSI/CAN/UL 325 must be designed and manufactured with features that help prevent someone being trapped beneath a closing door. One way of meeting that is an external entrapment protection device, which can be a photoelectric sensor, an edge sensor, or another system that passes the standard's test.

A photoelectric sensor, or photocell, uses one or more light beams to detect an obstruction in a detection zone. The common residential arrangement is a through-beam pair: an emitter on one side of the opening and a receiver on the other. Some units use a retro-reflective design instead, with the emitter and receiver in one housing and a reflector opposite.

Source: DASMA Technical Data Sheet [#364, Installation Location of Photoelectric Sensors on Residential Garage Doors](https://www.dasma.com/wp-content/uploads/2026/07/TDS364.pdf) (PDF). Checked 31 August 2026.

## Where they must sit

DASMA sets this out precisely, and it is worth checking against your own door because a surprising number of installations get it wrong:

- **Height.** Each photoelectric eye lens, or the lowest lenses where multiple sets are fitted, must be installed to emit a beam **no higher than six inches above the garage floor**: .
- **Spacing.** Sensors are usually located up to twenty feet apart, though this can be greater where the manufacturer's instructions allow it.
- **Distance from the door.** Sensors should sit **within six inches of the path of the door**: , measured perpendicular to the door.
- **And above all, the manufacturer's instructions govern.** DASMA is explicit that installation should in all cases follow the operator manufacturer's instructions, and that the manufacturer should be contacted if a variation is needed.

The six-inch height is not arbitrary. It is low enough to catch a small child lying down or a pet, which is the scenario the whole system exists for. Sensors raised to eighteen inches "so the leaves stop setting them off" are a defeated safety system, and we will move them back down.

**Never bypass, bridge or tape over the sensors.** DASMA's wording is that "to reduce the risk of severe injury or death, it is essential that photoelectric sensors be installed properly according to manufacturer's instructions." Bridging the terminals so the door closes without them removes the protection entirely while leaving the door looking normal.

## The two monthly tests

DASMA asks for both of these every month, on every residential door with an opener. Together they take about a minute.

### Test 1: the photo eyes

1. Start the door moving down.
2. Apply a controlled obstruction in the path of the beam. A broom handle held across the opening is ideal. Do not use your foot.
3. The door must reverse direction and return to the fully open position.

### Test 2: the reversing mechanism

1. Place a solid object about one and a half inches high on the floor in the door's path. DASMA's inspection checklist specifies a 1½-inch solid object such as a piece of two-by-four at least six inches long.
2. Close the door with the opener.
3. On contact with the object, the door must reverse.

If either test fails, stop using the opener until it has been looked at. A door that does not reverse is not a door with a minor fault.

Sources: DASMA [TDS-364](https://www.dasma.com/wp-content/uploads/2026/07/TDS364.pdf) (monthly testing procedure) and [TDS-167, Residential Sectional Garage Door and Electric Operator Checklist for Home Inspectors and Consumers](https://www.dasma.com/wp-content/uploads/2023/04/TDS167.pdf) (PDFs). Checked 31 August 2026.

## What a blinking sensor light is telling you

Most residential sensors have two LEDs, one on each unit. Exact colours vary by manufacturer, so check your manual, but the pattern is almost universal:

Reading the sensor LEDs | What you see | What it usually means | What to try |
| --- | --- | --- |
| Both LEDs steady | Aligned and clear. The sensors are not your problem. | Look elsewhere: travel limits, force settings, or a binding door. |
| Receiver LED flickering or off | Beam broken or misaligned. | Clear the beam path, wipe both lenses, and check nothing has knocked a bracket. |
| One LED completely dark | No power to that unit. | A pinched, stapled-through or corroded wire, or a loose terminal at the opener. |
| Both dark | No power to the sensor circuit. | Opener-side fault. Stop using the opener and call. |
| Door reverses only in bright sun | Direct sunlight washing out the receiver. | A real and common problem. Shields or repositioning within the allowed envelope fix it. |

## Reasons a door reverses that are not the sensors

- **Something in the beam you have stopped noticing.** A bin, a bike wheel, a coiled hose, a snow shovel leaning by the door.
- **Frost or condensation on the lenses**: , which is a January speciality on this lakeshore.
- **A binding door.** If the door drags on the way down, the opener reads it as an obstruction and reverses. That is a door problem, and turning the force setting up to mask it is the wrong fix and a dangerous one.
- **Travel limits set wrong,** so the opener thinks the door has hit the floor before it has.
- **A worn or debris-filled bottom seal**: compressing unevenly, which the opener feels as resistance.

## If your door has no sensors at all

Openers that predate external entrapment protection are still in service in this area, usually on garages that have not been touched in decades. There is no photo eye to test on those, and no way to add one to some units. If you have small children or pets and an opener with no eyes, that is the strongest case there is for replacing the opener rather than repairing it again.

## The other thing to test: the manual release

Once a year, with the door fully closed, pull the red release cord and lift the door by hand to check it can be operated manually. Use the handles or gripping points, never the joint between two sections: DASMA warns that "the section-to-section joint is not a suitable gripping point" and that gripping there "could result in serious injury". Residential sectional doors are required to have four handles or suitable gripping points, two inside and two outside, within eight inches of the bottom edge of the bottom section and on the second or third section.

Source: DASMA Technical Data Sheet [#165, Manual Operation of a Garage Door](https://www.dasma.com/wp-content/uploads/2025/05/TDS165.pdf) (PDF), summarising ANSI/DASMA 116 section 7. Checked 31 August 2026.

## Sources

1. DASMA Technical Data Sheet #364, *Installation Location of Photoelectric Sensors on Residential Garage Doors*. [dasma.com](https://www.dasma.com/wp-content/uploads/2026/07/TDS364.pdf) (PDF). Checked 31 August 2026.
2. DASMA Technical Data Sheet #167, *Residential Sectional Garage Door and Electric Operator Checklist for Home Inspectors and Consumers*. [dasma.com](https://www.dasma.com/wp-content/uploads/2023/04/TDS167.pdf) (PDF). Checked 31 August 2026.
3. DASMA Technical Data Sheet #165, *Manual Operation of a Garage Door*. [dasma.com](https://www.dasma.com/wp-content/uploads/2025/05/TDS165.pdf) (PDF). Checked 31 August 2026.
4. DASMA Technical Data Sheet #351, *Federal and State Garage Door Operator Legislation Guidelines for Dealers and Installers*. [dasma.com](https://www.dasma.com/wp-content/uploads/2024/01/TDS351.pdf) (PDF). Checked 31 August 2026.

### Door reversing on its own?

Run the two tests above first. If either fails, stop using the opener and call.

[Call (905) 536-5369](tel:+19055365369)

### The one-minute version

- Beam no higher than 6 inches off the floor.
- Within 6 inches of the door path.
- Both LEDs steady, lenses clean.
- Test the beam monthly.
- Test contact reversal monthly.
- Never bridge or bypass them.

[Opener repair service](https://www.garagedoorman.ca/services/garage-door-opener-repair/)

## Related

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Garage Doorman repairs and installs residential garage doors from Grimsby, Ontario. (905) 536-5369. Full site: https://www.garagedoorman.ca/