Why do the photo sensors of a garage door sit near the floor?

Photoelectric sensors are the non-contact layer of garage door entrapment protection, and their mounting height is specified because of who they exist to protect. Mounted within a few inches of the floor, the beam crosses the opening at a height that a crawling infant, a small child lying down or a pet will interrupt. Raise them and a gap opens beneath the beam — the door closes on anything low enough to pass under it, which is precisely the population the sensors were added to protect after contact-reversal alone proved insufficient. Sensors mounted high are a common field finding, usually because someone raised them to stop nuisance interruptions from debris, and the inspector reports the height as a defect even though the sensors test correctly when the beam is broken by a hand.

The sensors are mounted low so the beam crosses the opening at a height that intercepts a small child or a pet. Mounted higher, anything below the beam passes undetected and the door closes on it.

Automatic garage door openers include photoelectric sensors mounted near the floor across the opening, providing non-contact entrapment protection in addition to the force-reversing mechanism.

Low Enough to Catch a Toddler. Raise the beam and you have built a gap exactly the size of who it was protecting.

Test both protections separately — break the beam for the photo-eyes and obstruct the door for the reversing mechanism. Each can fail independently.

• •Testing the beam without checking mounting height
• •Accepting raised sensors because they were moved to stop nuisance trips
• •Testing only one of the two entrapment protections