What are gate loop detectors and do I need them?
A loop detector is a wire loop cut into the driveway that senses the metal mass of a vehicle. Gates commonly use up to three: an exit loop that opens the gate from inside, a safety loop that prevents closing on a vehicle, and a shadow loop that holds the gate open while a vehicle sits in the path.
How they work
A loop of wire is cut into a saw kerf in the driveway surface and sealed. The detector drives a small current through it and watches the loop's inductance; a vehicle's metal mass changes that inductance, and the detector reports a vehicle present. It is simple, has no moving parts, and is unaffected by weather, dirt, or sunlight — which is why it has outlasted a lot of newer ideas.
Because it senses metal mass, it does not detect people or animals. That is important: a loop is not a substitute for the entrapment protection required by the safety standard, per what UL 325 requires.
The three common loops
- Exit loop. Inside the gate; opens it automatically as a vehicle approaches from within.
- Safety loop. In the gate's path; prevents the gate from closing while a vehicle is there.
- Shadow loop. Directly under the gate's travel; holds the gate open so it cannot close on a stopped vehicle.
- Free-exit combinations that also prevent tailgating on commercial sites.
What goes wrong with them
Pavement movement is the main enemy. Oklahoma's expansive clay soils move driveways seasonally, and a loop in cracking or shifting concrete eventually breaks. The symptom is a gate that stops opening automatically on exit, or that closes when it should not — which is the behavior in a gate that stops halfway and sometimes in a gate that opens by itself.
Water intrusion into a poorly sealed kerf is the other, causing intermittent faults that track the weather. Detectors themselves can also drift and need re-tuning.
Do you need them
A safety or shadow loop is strongly advisable on any gate with vehicle traffic, and on commercial installations it is generally part of a properly protected system alongside photo eyes and edges — gate safety sensor requirements. An exit loop is a convenience, but a very popular one: nobody wants to get out of the car to leave their own property.
Alternatives exist where cutting pavement is impractical — probe and surface-mount detectors, and photo-based sensing. Our gate team diagnoses and replaces loops across the OKC metro, and estimates are free.
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Related Questions
What safety sensors are required on automatic gates?+
Two independent means of entrapment protection in every entrapment zone; that is the UL 325 standard every modern gate operator is built and listed to. Read the full answer →
Why does my automatic gate stop halfway?+
Because something told it to. Gates stop mid-travel when obstruction sensing trips (misaligned photo eyes, an over-sensitive force setting, debris in a slide track), when limit switches lose their position, or when a weak battery sags under load. Read the full answer →
Why does my automatic gate open by itself?+
Something is issuing a legitimate open command, just not from you. Read the full answer →
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