Garage Door Safety Sensors and Auto-Reverse: How They Work and the Monthly Test

Question 01

How do garage door safety sensors work?

One sensor sends an invisible infrared beam across the doorway, low down, and the other one catches it. If a toddler or the dog breaks that beam while the door's coming down, the opener stops the door and sends it back up. Block the beam before it starts and the door won't close at all.

The pair sit on each side of the opening, just off the ground. B&D's wireless beam manual puts the beam 100mm above the floor, as per AS/NZS 60335.2.95, and as close to the door opening as it'll go. B&D says the sensors switch on the moment the door starts to close.

Each sensor usually has a small light that shows whether the pair can see each other. What's normal depends on the brand. On Chamberlain's sensors, both lights glow steady when they're lined up. On B&D's wireless beams, the receiver's red light is on when the beam's clear and goes off when it's blocked.

Some beams are wired to the opener. Others are wireless and run on batteries. Worth knowing when they stop working out of nowhere.

Question 02

What's the difference between safety beams and auto-reverse?

Auto-reverse is built into the opener. It senses extra load when the door hits something and sends it back up. Safety beams are an add-on that spot something in the doorway before the door touches it. You want both. Auto-reverse only works after contact, and a garage door is heavy.

ATA's GDO-2 opener manual is blunt about it. For the opener to sense something in the doorway, the door has to press on it with some force, so whatever's there can still be hurt. That's why Merlin's MR800 manual calls its beams an extra measure of safety against a small child being caught under a garage door.

Question 03

Does my garage door have to have safety beams?

Not every door does. Opener manuals say beams must be fitted when the door closes with more than 400N of force at the bottom edge, about 40kg, when you run it from a phone app out of sight of the door, or when you use auto-close. They're strongly recommended for any home with young kids or pets.

The Australian and New Zealand safety standard for the motors that lift and lower home garage doors is AS/NZS 60335.2.95. The 2020 and 2024 editions are both current right now. The 2024 edition takes over fully on 29 November 2027.

Chamberlain says a November 2018 update to the standard made it clear that openers run from smart devices need monitored safety beams, with a changeover period that ended in November 2020. B&D says that from 1 December 2020, safety beams are compulsory with the sale of any smart opener. And Merlin's myQ app won't work until beams are fitted.

The 400N rule comes from both the Merlin MR800 manual and B&D's beam manual. The auto-close rule is in the Merlin, ATA and B&D manuals. On some openers, like the ATA GDO-2, beams are an optional extra, so not every home has them. Without beams, the auto-reverse is the only safety check, and the monthly test below matters even more. Not sure what yours has? Thom tests the opener and its safety reversal at every garage door service.

Question 04

How do I test the auto-reverse on my garage door?

Open the door, lay a piece of timber about 40mm thick flat on the floor in its path, then close it with the remote. It should touch the timber and go straight back up. Merlin and ATA both give this test in their opener manuals and say to do it once a month.

1. 01Clear the doorway. Kids, pets and the car out. Stand where you can see the whole door.
2. 02Lay the timber flat on the floor, right where the bottom of the door lands. A 40mm offcut is what the Merlin MR800 and ATA GDO-2 manuals use. At that height it should sit under the beam, if you have one, so you're testing the opener itself.
3. 03Close the door with the remote or wall button and watch it all the way down.
4. 04It should reverse the moment it touches the timber. If it stops and sits there, presses down on it or keeps trying to close, it's failed. Use the remote to send it back up.
5. 05Take the timber away and jot down the date. Same again next month.

B&D's version uses a roll of paper towel under the door. If the door doesn't reverse as soon as it touches the roll, B&D says to book a service. Same idea either way. The door should bounce back up on contact and never squash what's under it.

Question 05

How do I test the safety beams?

Start the door closing, then block the beam with something solid, like a cardboard box, while you stand clear. The door should stop and head back up. Then try closing it with the beam still blocked. It shouldn't close. B&D's beam manual asks owners to run this check from time to time.

1. 01Open the door fully and clear the doorway.
2. 02Look at the lights on both sensors. Your manual says what normal looks like for your brand.
3. 03Press close. Once the door's moving, slide a cardboard box into the doorway in line with the sensors. Keep yourself out of the door's path.
4. 04The door should stop and go back up straight away.
5. 05Leave the box there and press close again. Merlin's MR800 manual says the beams stop an open door from closing, so it shouldn't budge.

If the door keeps coming down with the beam blocked, the beams aren't protecting anyone. Keep kids and pets well clear of the doorway and book a garage door repair. The auto-reverse is then the only thing between the door and whatever's under it, so test that too.

Question 06

Why do the safety beams stop my door closing when nothing's there?

Usually something's in the beam that you can't see, or the sensors can't see each other. Dust or a spider web on a lens, a sensor bumped by the bin or the mower, low sun shining into the receiver, or flat batteries in wireless beams will all do it. Most of these you can check yourself.

• Dirty lens. B&D's beam manual says to clean both lenses if the beams live somewhere dusty. Wipe them gently and clear away any spider webs.
• Knocked out of line. A bin, a bike or a car bumper can nudge a sensor. Chamberlain says one light off or flickering usually means the pair are out of line or blocked. Its fix is to loosen the sensor's wing nut, aim it at the other one until the light glows steady, then tighten it again.
• Low sun. Chamberlain says sun shining straight into the receiving sensor can block the beam. The door opens fine but won't close while the sun's on that sensor. B&D's manual says to put the receiver in the shade.
• Flat batteries. Wireless beams run on batteries. On B&D's wireless beams, the opener light flashes four times at the start and end of each run when they're getting low.
• A loose or broken wire on wired beams. Chamberlain lists this one too. That's a job for a technician.
• Nothing to do with the beams. ATA's manual says very strong wind pushing on a door can set off the opener's safety system now and then. It also lists a door gone stiff and tight in its tracks as a reason it reverses.

Still stuck after a wipe and a look? Garage door won't open or close goes through the other common faults.

Question 07

What should I do if my garage door fails the safety test?

Stop using the opener. ATA's manual says not to use a door that won't reverse when it hits something until it's been fixed and tested again. Keep kids and pets clear and call a technician. If you need the door before then, run it by hand with the manual release. Don't turn up the force yourself.

A door can fail the test for more than one reason. The opener's settings may be off, or the door itself may be stiff, out of balance or down a spring. Merlin's MR800 manual says never to let the opener make up for a door that sticks or binds, and that too much force stops the safety reverse working properly. Both are technician jobs.

To use the door by hand in the meantime, see how to open a garage door manually. Do it with the door shut. If it feels very heavy or won't stay up, leave it and call.

On a repair, Thom checks the whole door as well as the opener, whether you're in Baringa, Bells Creek or anywhere else on the Sunshine Coast. Garage door repairs covers what he fixes. Repairs and servicing are booked as a callout valued between $200 and $300 depending on the door size and the labour involved. What the callout covers is in garage door service and repair costs. Call 0402 882 653 or book a callout.

Question 08

How do I keep kids and pets safe around an automatic garage door?

Keep remotes and the wall button out of their reach, and never let them play with either. Only run the door when you can see it, and teach kids to wait in one safe spot while it closes. Test the auto-reverse monthly, and have safety beams fitted if you've got little ones or a dog.

Kidsafe WA says garage injuries to children most often involve fingers caught in doors, or kids trapped by a garage door or electric gate. Its advice is to set up a safe spot for kids to stand while the door closes, and to always watch them around a closing door.

• Wall button up high. The Merlin MR800 manual says to fit it at least 1.5m off the floor, where you can see the door, away from moving parts.
• Remotes out of reach. The same manual says not to let children use the remotes or buttons, or play near the door.
• Nobody walks under a moving door. Merlin says no one should go in or out of the garage while the door's moving.
• Door right up before you drive. ATA's manual says to make sure the door's fully open before you drive in or out, and fully shut before you leave the driveway.
• Pets count. B&D says its beams stop and reverse the door for a child, a pet or a car, and strongly recommends them if you have kids or pets.

Running the door from a phone app? That's when beams matter most, because you may not be able to see the doorway at all. It's also why smart openers need them.