# Inherited an old garage door opener? How to tell if it has safety sensors > Inherited an old garage door opener? Learn how to check for the photo eyes and auto-reverse the federal safety rule requires, and what to do if it lacks them. Source: https://garagedoorscience.com/blog/old-garage-door-opener-safety-sensors · by margaret · published 2026-11-05 You moved into the house, and the garage door opener came with it. It still lifts the door and lowers it. What you do not yet know is whether it will stop and go back up when something is in the way. You can find that out yourself, from the floor of your garage, without touching anything that is under tension. This article shows you what to look for, how to test it, and what to do if the opener does not pass. ## What the federal rule asks every opener to do The rule for residential garage door openers is 16 CFR part 1211. It requires two independent protections on every opener. The first reverses the door when it makes contact with an obstruction. The second is a [secondary entrapment protection device](https://garagedoorscience.com/blog/garage-door-safety-sensors), which is either an external photoelectric sensor, usually called a photo eye, or an edge sensor. Two, because [no single system is meant to be the only line of defense](https://garagedoorscience.com/blog/garage-door-auto-reverse-mechanism). The contact protection also has a deadline. Under 16 CFR 1211.7, a closing door must [begin to reverse within 2 seconds of contact](https://garagedoorscience.com/blog/garage-door-auto-reverse-mechanism) with an obstruction. ## How the opener knows it hit something There is no force sensor and no strain gauge. The opener watches the current draw of its own motor. When the door meets resistance, that current spikes, and when it [rises above a threshold set during force learning](https://garagedoorscience.com/blog/garage-door-auto-reverse-mechanism), the opener reverses. On an opener you inherited, someone else set that threshold, and you do not know when it was last checked. The test later in this article tells you whether it still works. The photo eyes work differently. One unit sends a [modulated infrared beam from an emitter to a receiver](https://garagedoorscience.com/blog/garage-door-safety-sensors). Because the beam is modulated, the receiver ignores ambient light such as sunlight, heat lamps and car headlights. The [safety systems lab](/labs/safety-systems-lab) walks through how the two protections fit together. ## Look for the photo eyes Stand inside the garage and look at the bottom of the door opening, on both sides, near the tracks. Photo eyes [sit about 6 inches above the floor](https://garagedoorscience.com/blog/garage-door-repair-guide), one on each side, facing each other across the path of the door. If you are not sure what the tracks and brackets around them look like, the [garage door anatomy lab](/labs/garage-door-anatomy) labels each part. If you find a pair, your opener has a secondary device. Move on to the test. If you find no photo eyes, the opener may use an edge sensor instead, the other device the rule accepts. If you can find neither, treat the opener as having one protection at most. The rule asks for two. ## What a working sensor does, and how a Chamberlain tells you When the photo eyes are [misaligned or blocked](https://garagedoorscience.com/blog/garage-door-repair-guide), the door stops closing before it reaches the floor and reverses open. So if your door keeps coming back up on its own, that can be the sensors reacting to something in the beam, or a pair knocked out of line. On a Chamberlain B980, [ten flashes of the opener light while the door reverses on closing](https://garagedoorscience.com/blog/garage-door-opener-light-blinking-patterns) means the beam was obstructed or the sensors are misaligned. That pattern belongs to that model. If yours is a different opener, its own manual gives its own codes. ## Test the reversal the way Chamberlain's manual says Chamberlain's installation manual gives a reversal test for its openers. If you have a Chamberlain, follow it. If you have another brand, follow that maker's manual instead. Before you run the opener at all, the manual says to [disable ALL locks and remove ALL ropes connected to the garage door](https://cgi.widen.net/content/vlzppckqt9/original/114a5126.pdf), to avoid entanglement. Check for both. Then run the test: 1. Lay a 2x4 flat on the floor in the middle of the door's path. The manual states that the [garage door MUST reverse on contact with a 1-1/2" (3.8 cm) high object, or a 2x4 laid flat](https://cgi.widen.net/content/vlzppckqt9/original/114a5126.pdf), on the floor. 2. Close the door with the wall control or the remote. 3. Watch the door meet the board. It must reverse. If the door touches the board and reverses, the contact protection is working. If it presses down on the board, stops without reversing, or does not reverse at all, it has failed the test. Do not keep using it as though it passed. The manual also says the [safety reversal system MUST be tested every month](https://cgi.widen.net/content/vlzppckqt9/original/114a5126.pdf), and that [after ANY adjustments are made, the safety reversal system MUST be tested](https://cgi.widen.net/content/vlzppckqt9/original/114a5126.pdf). This first test is the start of a habit, not a one-time check. If you open the opener's cover to look for a model label, the same manual says to [ALWAYS disconnect electric and battery power to the garage door opener BEFORE making ANY repairs or removing covers](https://cgi.widen.net/content/vlzppckqt9/original/114a5126.pdf). ## What you leave alone The opener sits on a door system balanced by springs and cables. Chamberlain's manual is direct about it: [ALL repairs to cables, spring assemblies and other hardware, ALL of which are under EXTREME tension, MUST be made by a trained door systems technician](https://cgi.widen.net/content/vlzppckqt9/original/114a5126.pdf). Looking for photo eyes and running a board test is yours to do. Anything that involves the springs, the cables or the hardware holding them is a trained technician's job. The [spring safety introduction](/videos/spring-safety-intro) explains what those parts are, so you know what not to reach for. ## If your opener has no sensors or fails the test HomeAdvisor puts the normal range for installing a garage door opener at [$218 to $540, with an average of $379](https://garagedoorscience.com/blog/garage-door-opener-cost-breakdown), and a typical opener quote includes one set of safety sensors. When you get a quote, ask to see the sensors listed on it. If you would like someone to look before you decide, [A+ Garage Doors (our affiliated installer)](https://aplusgaragedoor.com/) is one place to start, and [Garage Door Pro Services (our affiliated installer)](https://garagedoorproservices.com/free-garage-door-safety-inspections-by-garage-door-pros/) has a page titled Free Garage Door Safety Inspections. For more on how the two protections are tested and why each one exists, see the [garage door safety guide video](/videos/margaret-garage-door-safety-guide). ## What to do today - Look at both sides of the door opening, about 6 inches above the floor, for a pair of photo eyes. If there are none, look for an edge sensor. - If you have a Chamberlain, disable any locks, remove any ropes, and run the 2x4 test from its manual. If you have another brand, find that maker's manual and use its test. - If the opener has neither sensor, or the door does not reverse on the board, get a quote for a replacement opener and confirm the sensors are included. - Put a monthly reminder on your phone to repeat the reversal test. The checking is yours. The springs and cables belong to a trained technician. An opener that will not reverse is one to fix before you trust it again.