In the past, occupancy sensors were often evaluated by detection range, coverage, sensitivity, and accuracy. Those factors still matter, but they are not enough for a real building automation project.

A useful occupancy sensing solution needs to answer three practical questions:

• What is the current state of the space?
• Is that state reliable enough to trigger automatic control?
• How will occupancy information be delivered to lighting, HVAC, or BMS?

For this reason, the next stage of occupancy sensing is not only about stronger detection. It is about building the full control chain from space sensing to building response.

What Is Occupancy Sensing?

Occupancy sensing uses sensor technology to determine whether a space is being used, then provides presence, activity, or space-use information to other systems.

Traditional motion sensors mainly trigger from obvious human movement. More advanced presence sensors need to recognize occupancy even when a person is relatively still, such as working, meeting, reading, or resting.

With the development of 24GHz and 60GHz mmWave sensing technology, occupancy sensing can provide more types of information, including:

• Presence detection
• Motion detection
• Quiet occupancy detection
• People counting
• Position detection
• Zone detection
• Trajectory information

This means the role of an occupancy sensor is gradually changing from a simple switch trigger into a source of space-state data.

How Occupancy Sensors Are Used in Building Automation

An occupancy sensor can provide real-time space status to lighting control, HVAC, ventilation, BMS, or an IoT platform. The building can then respond to actual use instead of relying only on a fixed schedule.

In a meeting room, lighting can turn on when people enter. If people remain seated quietly, presence detection can help the system maintain the occupied state.

In an office, HVAC can adjust operation according to real space usage instead of running in vacant areas only because the schedule says so.

In a public restroom, the system can control lighting and exhaust based on actual occupancy, while reducing the risk of turning equipment off too early when someone is still inside a stall.

In a hotel room, occupancy information can help the system better distinguish temporary activity changes from a truly vacant room, improving the balance between comfort and energy saving.

The value of occupancy sensing is therefore not only to tell the system:

More importantly, it tells the building:

Presence Detection vs. Occupancy Detection

Motion detection, presence detection, and occupancy detection are often discussed together, but they do not solve exactly the same problem.

For building automation, the final requirement is usually not more motion events. It is a more stable and reliable occupancy state.

Why Quiet Occupancy Matters

People in meeting rooms, offices, hotel rooms, and similar spaces are not always making obvious movements.

When someone is using a computer, reading, having a meeting, or resting, they may remain relatively still for a long period of time.

If the system relies only on obvious motion, it can create this control problem:

The result may be lights turning off too early, or other equipment entering energy-saving mode at the wrong time.

Occupancy sensing therefore needs to detect entry quickly and also handle quiet occupancy reliably. This is one reason why mmWave presence sensing is receiving more attention in indoor building automation applications.

Why Detection Boundary Can Be More Important Than Range

Many occupancy sensors emphasize longer detection range. In real building automation projects, however, longer range does not always mean better control.

For example, if a meeting room sensor also detects people passing through the corridor outside the door, the sensor may not be "wrong" from a pure detection perspective. But from the viewpoint of meeting room lighting control, it can still create an unwanted trigger.

That is why sensor selection should not only ask:

It should also ask:

Detection boundary, zone configuration, exclusion area, and installation position may directly affect the final control result.

For smart buildings, a clearly defined detection zone is often more valuable than simply pursuing a larger detection range.

People Counting for HVAC and Ventilation

Presence detection usually answers: "Is anyone here?" People counting goes one step further and answers: "How many people are here?"

For lighting control, occupied or vacant status is often enough. For HVAC and Demand-Controlled Ventilation (DCV), people-count information may provide additional value.

A meeting room with two people and the same room with fifteen people are both occupied, but the ventilation and environmental-control requirements can be very different.

If the occupancy sensing system can provide real-time people-count information, the BMS has an opportunity to create a more dynamic control strategy based on actual occupancy load.

Moving from presence detection to people counting is therefore not just adding another data point. It can change how occupancy data is used in building automation.

Building Automation Interfaces Matter

A sensor can recognize space status accurately, but that does not mean the building can use the information immediately. Occupancy data still needs to enter the control chain.

Depending on the building automation architecture, common connection and control options may include KNX, DALI, BACnet, Modbus, MQTT, 0-10V, relay, and other building IoT interfaces.

Different protocols are suitable for different system architectures. No single communication method covers every project.

The more important question is:

Lighting control may only need occupied or vacant status, or a dimming control signal. HVAC or BMS may need occupancy state, people count, or richer data. An IoT platform may also need real-time upload, historical records, and integration with other systems.

For this reason, sensor selection in a building automation project should not consider sensing technology alone. It should also consider data output and communication interface from the system architecture level.

Cloud or Local Control?

For real-time building automation, cloud and local processing should not be treated as a simple either-or choice.

Local processing is better for real-time response.

For example, turning on lights when people enter, or notifying the local building control system after occupancy status changes. These functions require low latency and should continue to work even if the internet connection is temporarily interrupted.

Cloud is better for long-term analysis and cross-system management.

Examples include space-utilization analysis, historical occupancy trends, multi-building management, device management, and further data optimization.

A more practical architecture is:

The final architecture still needs to be designed around project requirements for reliability, latency, data security, and system integration.

How to Choose an Occupancy Sensor for Building Automation

In real projects, it is usually better not to start with "which sensor has the longest detection range?" A more effective approach is to define the application first.

At minimum, the project should clarify the following points:

1. What needs to be recognized? Motion, presence, quiet occupancy, or people counting?
2. Which areas should be detected? Should the whole room be covered, or does the project need independent zone detection? Should the corridor or adjacent area be excluded?
3. What will people do in the space? Is there long-duration quiet work, meetings, resting, or other low-motion activity?
4. What will the occupancy state control? Lighting, HVAC, ventilation, BMS, or an IoT platform?
5. What interface does the system need? Relay, 0-10V, KNX, DALI, Modbus, MQTT, or another communication method?
6. Which error matters more? Incorrectly judging the space as vacant while people are still inside, or triggering from outside activity when nobody is using the space?

After these questions are clear, it is easier to decide the sensing technology, detection range, installation position, and protocol.

The Role of 24GHz and 60GHz mmWave

Different sensing technologies are suitable for different levels of building automation.

For some applications, 24GHz mmWave can be used for presence detection, micro-motion detection, and more refined zone control.

When a project needs people counting, position, or trajectory information, 60GHz mmWave can provide richer spatial data capability.

However, frequency itself is not the only standard for judging whether a solution is good. Real selection should follow this logic:

The most valuable sensing solution is the one that fits the actual control requirement, not simply the one with the highest frequency.

Where Occupancy Sensing Is Going

Occupancy sensing is moving through three stages:

• Motion Detection: "Did something move?"
• Presence Detection: "Is someone still here?"
• Occupancy Intelligence: "How is this space actually being used, and how should the building respond?"

As sensing technology, edge processing, and building automation integration continue to develop, occupancy data will no longer be only an isolated sensor output. It can become an important input for lighting, HVAC, ventilation, and BMS decisions.

When evaluating an occupancy sensing solution, the question should not only be:

It should also be:

A truly intelligent building is not defined by having more sensors or producing more data. It is defined by how well it responds to the real state of the space, at the right time, with the right control action.