# How your door knows to stop and go back up

Source: https://garagedoorscience.com/academy/how-your-garage-door-works/how-the-door-knows-to-stop · part of [How your garage door works, and what to do when it does not](https://garagedoorscience.com/academy/how-your-garage-door-works) · 4 min

You press the button and walk away. The door comes down behind you. So what stops it from coming down on a child, a dog, or the bike you left in the doorway?

Your opener has two ways to tell.

The first is built into the opener itself. Genie, an opener maker, calls it the internal contact reverse mechanism. If the closing door touches something, it turns around.

The second sits outside the opener. Genie describes these as infrared sensors or sensing edges. The federal rule, 16 CFR 1211, spells out what a photoelectric sensor, the photo eye near the floor, has to do. If it is set off while the door is closing, the door reverses, goes all the way back up, and stops there. And the sensor keeps the opener from closing an open door.

## The 1993 line

The federal rule applies to every home garage door opener made on or after January 1, 1993 for sale in the United States. Genie explains that the Consumer Product Safety Commission put these rules into law, so openers made after 1992 had to have an outside sensor as well as the contact reverse.

Openers made before that are a different story. Genie says the vast majority of them have no infrared sensors or anything like them, so they do not meet today's standard, and it advises replacing a pre-1993 opener, not repairing it.

If your opener is that old, take it seriously. Without an outside sensor, the door has to touch someone before it turns around.

One more thing can get in the way. Chamberlain, an opener maker, says an unbalanced garage door may not reverse when required. Balance comes from the springs, and springs are always a technician's job. If you think your door is out of balance, do not try to fix it yourself. Have a technician check it.

## Try this

If your door will not close, or stops and goes back up for no reason you can see, tell [the Virtual Technician](/diagnose) what the sensor lights are doing. It asks a few questions and tells you what it points to.

## Go further

- Lab: [Safety Systems Lab](https://garagedoorscience.com/labs/safety-systems-lab)
- Video: [How to fix garage door eye sensor](https://garagedoorscience.com/videos/fix-garage-door-eye-sensor)
- Article: [How garage door safety sensors actually work](https://garagedoorscience.com/blog/garage-door-safety-sensors)
- Article: [How garage door auto-reverse works and how to check yours](https://garagedoorscience.com/blog/garage-door-auto-reverse-mechanism)

## Sources

- [16 CFR Part 1211, Safety Standard for Automatic Residential Garage Door Operators](https://www.ecfr.gov/current/title-16/chapter-II/subchapter-B/part-1211)
- [PRE-1993 OPENERS SHOULD BE REPLACED - NOT REPAIRED](https://www.geniecompany.com/policy-pages/pre-1993-openers)
- [How to test the balance of a garage door](https://support.chamberlaingroup.com/s/article/How-to-test-the-balance-of-a-garage-door-1484145605074)