You're right, occupancy sensors can be tricky, especially in a doorway situation. Here's a breakdown of the best occupancy sensor types for a school lunchroom entrance, considering your need to avoid triggering from outside the room

The Best Option: Ultrasonic Sensor with Narrow Field of View
How it Works

Ultrasonic sensors emit high-frequency sound waves and detect movement by changes in the reflected waves.

Why it's good for your situation



Directional Control

Ultrasonic sensors can be selected with a very narrow field of view. This is critical for your open doorway. You can aim it specifically within the lunchroom entry area.

Sensitivity Adjustment

Many ultrasonic sensors have adjustable sensitivity. You can fine-tune it to only detect movement closer to the sensor and ignore movement further away (like in the hallway).

Less Susceptible to Environmental Factors

Generally less prone to false triggers from drafts, temperature changes, or reflections than some PIR sensors.

Other Options to Consider (with caveats)



Dual Technology (PIR + Ultrasonic)



How it Works

Combines both Passive Infrared (PIR) and Ultrasonic technologies. It only activates when both sensors detect movement.

Why it might work

The requirement of both technologies detecting movement could reduce false triggers.

Caveats

Still might trigger if someone pauses briefly in the doorway or just outside, especially if the PIR portion has a wide field of view. Requires careful aiming and sensitivity adjustment.

Occupancy Sensor Types to AVOID or use with Extreme Caution



Passive Infrared (PIR) with Wide Field of View



How it Works

Detects changes in infrared (heat) radiation.

Why it's problematic

PIR sensors often have a wide field of view. They are easily triggered by people walking by in the hallway. Even with masking, it can be difficult to prevent triggers from outside the doorway.

Why to avoid: PIR sensors often detect temperature changes, so they are not ideal for lunch rooms, because the sensor might detect kids getting hot lunches. Microphonic (Sound Activated) Sensors



How it Works

Detects sounds within the room.

Why it's problematic

School lunchrooms are noisy environments. A sound-activated sensor would likely stay on constantly.

Door Contact Switch



How it Works

The light is on when the door is open, off when the door is closed.

Why it's problematic

It is an open doorway.

Important Considerations Before Purchasing



Field of View

The most crucial specification. Look for a sensor that specifically allows for a very narrow, adjustable field of view. Check the sensor's spec sheet for a diagram illustrating its coverage pattern.

Sensitivity Adjustment

Ensure the sensor has a sensitivity adjustment that allows you to dial down the detection range.

Mounting Location

Mount the sensor carefully. Aim it to cover the immediate entry area of the lunchroom, avoiding any coverage of the hallway. Consider mounting it above the doorway, angled slightly downwards.

Masking/Lens Covers

Some PIR (though I don't recommend them) and dual-tech sensors come with masking kits or lens covers. These allow you to block off segments of the sensor's field of view, preventing detection in unwanted areas.

Test Before Permanently Mounting

After installation, thoroughly test the sensor to ensure it's not being triggered by people in the hallway. Adjust the sensitivity and masking as needed.

Recommendations

I suggest purchasing an Ultrasonic Sensor with Narrow Field of View. It is important to adjust the sensitivity and FOV after it is installed.Consult the installation instructions of the sensor for the correct adjustments.By focusing on sensors with adjustable and narrow fields of view, you can significantly reduce the chances of false triggers and ensure the lighting responds appropriately to people entering the lunchroom. Flag for review