Direct answer: A barrier photocell is a safety sensor made up of a facing transmitter and receiver that sends a signal to the control board when the invisible infrared beam between them is broken. If the beam is broken by a vehicle, person, or object during the arm's closing motion, the barrier stops closing or reopens, reducing the risk of a collision or entrapment.
How does it work?
A photocell pair consists of two separate units — one sends the beam (transmitter), the other detects it (receiver) — usually mounted facing each other on either side of the line the barrier arm travels. As long as the beam is uninterrupted, the system considers the path "clear"; the moment it's broken, an "obstacle present" signal is sent to the control board.
Where and how is it mounted?
In a standard installation, the photocell pair is placed along the line the arm travels, at a height close to arm level. At entrances with heavy pedestrian traffic as well, a second photocell pair can be added at a lower level to also detect children or small objects.
Using a photocell together with a loop detector
A photocell detects an instantaneous obstruction on the beam line, while a loop detector continuously detects a vehicle standing on the ground. When the two systems are used together, both a sudden obstruction entering the beam line while the arm is closing and a vehicle waiting under the arm are safely detected. Details on this are covered in our loop detector guide.
Quick facts table
| Operating principle | Signal generated by an infrared beam being broken |
|---|---|
| Typical mounting height | Close to arm level, on two facing posts |
| Pedestrian safety | A second, lower photocell pair can be added |
| Used together with | Works complementarily with a loop detector |
Frequently asked questions
What does a barrier photocell do?
It stops or reopens the barrier if the beam is broken by a vehicle or person while the arm is closing.
Where is a photocell mounted?
It is mounted on two facing posts along the line the arm travels, at a height close to arm level.
Last updated: July 20, 2026 · Technical content: Gray Teknoloji project team
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