Commercial Occupancy Sensor Buying Guide

Picking the right occupancy sensor is mostly about matching the detection technology and mode to the room. Get it wrong and you get lights that cut out on people sitting still, or lights that trip on from a passing draft. This guide walks through the occupancy sensor types, the occupancy-vs-vacancy decision, mounting and coverage, and the Title 24 code context that drives many of these choices in commercial buildings.

Rock Lighting & Electric is an authorized Legrand Wattstopper dealer, so the product references below point to Wattstopper lines we stock and support.

PIR vs. ultrasonic vs. dual-technology

The detection technology determines what kind of motion the sensor "sees." There are three core types.

PIR (passive infrared). PIR sensors detect the heat signature of people moving across the sensor's field of view. They are reliable, affordable, and resistant to false trips from non-human sources like HVAC airflow. The trade-off is that PIR needs line of sight and is best at detecting motion moving across its view rather than directly toward it. Blocked sightlines (partitions, tall shelving, stalls) reduce reliability. Good fit: open offices, hallways, warehouses, and other spaces with clear sightlines.

Ultrasonic. Ultrasonic sensors emit sound waves and measure how they bounce back, which makes them very good at picking up minor motion — typing, a small shift in posture — and at filling in spaces where line of sight is obstructed. The trade-off is that they are more prone to false-on triggers (for example, air movement) and need to be commissioned/tuned for the specific space. Good fit: restrooms, spaces with partitions or obstructions, and rooms where people stay relatively still.

Dual-technology (DT). Dual-tech sensors combine PIR and ultrasonic. The typical logic requires both technologies to detect motion to turn lights on, but only one to keep them on. That combination reduces false-on events (a draft alone will not trigger it) and false-off events (lights stay on for someone sitting still at a desk). Good fit: conference rooms, classrooms, and any space where both false-on and false-off are a concern. Wattstopper's dual-tech lines include the DT-300 series ceiling sensors (e.g., DT-300/DT-305 24VDC low-voltage and DT-355 100–347 VAC line-voltage) and the DLM digital LMDC-100 dual-tech ceiling sensor. (Sources verified below.)

Occupancy vs. vacancy sensors

This is a separate decision from the detection technology — it is about how the lights turn on.

• Occupancy (auto-on/auto-off): Lights turn on automatically when someone enters and turn off automatically after the space is vacant. Best for spaces where hands-free is the goal — hallways, restrooms, warehouses.
• Vacancy (manual-on/auto-off): The occupant turns lights on manually (a wall switch/button), and the sensor turns them off automatically once the space is empty. This saves more energy because lights never come on if no one flips the switch, and some code situations specifically call for manual-on. Best for offices and private rooms where daylight is often enough.

Many Wattstopper sensors and switches support both modes; the mode is set during installation/commissioning.

Mounting and coverage

Match the mounting type to the room geometry. Coverage area depends on the specific model and lens, so always confirm the published coverage for the exact SKU and ceiling height before specifying.

• Ceiling mount (360°): The most common commercial choice for centered, all-around coverage in offices, conference rooms, and classrooms. Wattstopper DT-300/DT-355 dual-tech and DLM LMDC-100 are ceiling-mount examples.
• Wall-box / wall-switch mount: Replaces a standard switch; sensor and control in one device. Good for small enclosed rooms, private offices, and retrofits where you do not want to run new wiring to the ceiling.
• High-bay: Lens optimized for tall mounting heights in warehouses, gyms, and industrial spaces. Wattstopper offers a DLM PIR high-bay ceiling sensor for these applications.
• Corner mount: Aimed down and across from a corner — useful for narrow rooms, stairwells, and spaces where a ceiling-centered unit would not cover the layout. Wattstopper offers DLM corner-mount PIR sensors.

Rule of thumb: pick the mount that puts the sensor's strongest coverage where people actually move, then verify the manufacturer's coverage chart for that lens and ceiling height (coverage square-footage and detection range vary by SKU and lens — confirm on the individual Legrand product/spec page).

Title 24 context (California)

If you are building or renovating in California, occupant sensing is not optional in many spaces. Under California's Title 24, Part 6 energy code:

• Occupant sensing controls are required in specified space types — including specified offices, multipurpose rooms, classrooms, conference rooms, and restrooms — to automatically shut off lighting after the space is unoccupied (within 20 minutes or less of the zone going vacant).
• Multilevel/continuous dimming: Where multilevel control is required, general lighting in qualifying spaces must generally be capable of continuous dimming from 100% down to 10% (or lower) of full-rated lighting power, with exceptions (for example, restrooms, healthcare facilities, single-luminaire spaces, and certain HID/induction sources that instead require a control step).

This is general guidance, not a compliance determination. Code specifics depend on space type, size, and the current adopted edition — confirm requirements with your AHJ or a Title 24 consultant. (See Energy Code Ace, below.)

How to choose

A short decision path:

1. Start with the room. Clear sightlines and motion across the space → PIR. Obstructions, partitions, or people sitting still → ultrasonic. Want the fewest nuisance events and budget allows → dual-tech.
2. Pick the mode. Hands-free, high-traffic → occupancy (auto-on). Maximum savings or manual-on required by code → vacancy.
3. Pick the mount. Centered open room → ceiling 360°. Small enclosed room/retrofit → wall-box. Tall ceiling → high-bay. Awkward geometry → corner.
4. Check code. In California, confirm Title 24 occupant-sensing and dimming requirements for your space type.
5. Verify coverage. Confirm the published coverage area for the exact model and ceiling height.

Work with an authorized Wattstopper dealer

Rock Lighting & Electric is an authorized Legrand Wattstopper dealer with contractor pricing on the DT dual-tech and DLM digital sensor lines. Browse our Wattstopper collection or contact us for spec help, code questions, and a quote sized to your project.

FAQ

This article is general guidance, not a substitute for the manufacturer's current documentation or the adopted code for your project. Confirm specifications, compatibility, and code requirements for your specific application before purchase or installation.