By the SightShield team · · 3 min read
How a loop detector works
A loop detector uses a coil of wire cut into the road surface. The loop forms part of an electrical circuit oscillating at a set frequency. When a large metal object — a car, bike or truck — stops over the loop, the frequency changes. The detector senses the change and switches a relay, telling the gate or barrier controller that a vehicle is present.
The jobs loops do
| Loop type | Where | What it does |
|---|---|---|
| Safety / presence loop | Under the boom or in the gate opening | Keeps the barrier up or the gate open while a vehicle is there |
| Exit loop | Inside the gate, before the exit | Opens the gate automatically for vehicles leaving |
| Closing / arming loop | Just past the barrier | Closes the barrier once the vehicle has passed |
Two-wheelers need special care
Indian gates see far more motorcycles and scooters than cars. Two-wheelers have much less metal close to the road surface, so a loop sized for cars may not detect them reliably. Loop shape, size, position in the lane and the detector’s sensitivity all affect two-wheeler detection. Where two-wheelers must be detected, the installer should test with real bikes during commissioning — and photocells remain essential for safety, because a loop that misses a bike will also miss a rider on foot.
Loops cannot see people
A loop only responds to metal vehicles. It will not detect a pedestrian, a child or an animal under a boom or in a gate opening. That is why barriers and gates in apartments and offices need photocells as well as loops: the loop protects vehicles, the photocell protects people.
Gate safety sensors explained →Loop shapes and layouts
- Rectangular loops are the standard choice for a single lane.
- Figure-of-eight loops reduce interference from nearby cables and adjacent loops.
- Arming loops before a barrier tell the system a vehicle is present for a card or ANPR read.
- Safety loops directly under the boom prevent it closing on a vehicle.
- Exit loops on the inside open the gate automatically for vehicles leaving.
Installation tips
- Loops are cut into concrete or asphalt and sealed; plan them before new paving if possible.
- Size and position the loop for the vehicles you need to detect, including two-wheelers if required.
- Keep loops away from steel reinforcement close to the surface, drainage covers and other loops, which can cause interference.
- Adjacent loops should run at different frequencies.
- Check sensitivity settings during commissioning with real vehicles.
Paver block driveways
Many Bangalore apartments and villas have interlocking paver driveways, where cutting a slot is not possible. Pre-formed loops — loops already sealed in a protective jacket — can be laid in the sand bed under the pavers when the driveway is laid or relaid. Plan them before the paving work, with a conduit for the loop feeder back to the barrier or gate controller.
Where loops add the most value
In apartments and offices, a safety loop under every boom barrier is essential. Exit loops make outgoing traffic smooth, so residents do not need a remote to leave. In factories, loops at the gate can also trigger cameras to capture each vehicle.
Boom barriers and gate automation →Quick answers
Does a loop detector detect motorbikes?+
It can, if the loop is sized and positioned for two-wheelers and the sensitivity is set correctly.
Can a loop detector replace photocells?+
No. Loops detect only vehicles; photocells are needed to protect people.
Can loops be added to an existing driveway?+
Yes. A narrow slot is cut into the surface, the wire laid in it and sealed.
Why does my boom barrier not open for scooters on the exit loop?+
The loop may be too large, poorly positioned or set at low sensitivity for two-wheelers. A technician can adjust sensitivity or reconfigure the loop.
How long does a loop last?+
A properly cut and sealed loop can last many years; failures usually come from road damage, digging or poor sealing.