Occupancy Sensors: Technology Makes Spaces More “Attentive” to You
Want to make your home or office smarter? The first step is to enable it to “sense” your presence! No more having the air conditioner blast into an empty room, or lights wasting energy in unoccupied corners. Choosing the right sensors is the cornerstone of achieving smart spaces. Below are some of the most popular and efficient room‑occupancy sensing technologies available today:

Motion sensor (core component):

Passive Infrared Sensor (PIR): The most widely used and cost-effective option. It detects motion by sensing changes in the specific wavelength of infrared thermal radiation emitted by the human body. Advantages: low power consumption, mature technology, and low cost.

Drawbacks: Ineffective on stationary individuals; susceptible to interference from heat sources; limited detection range, angle, and sensitivity.

Microwave radar sensors actively transmit microwave signals—typically at 24 GHz or 60 GHz—and detect motion, including subtle movements such as breathing and heartbeat, by analyzing the Doppler frequency shift of the reflected echoes or the time-of-flight (ToF).

Advantages: Can penetrate non-metallic materials (such as thin walls, glass, and plastic); capable of detecting stationary targets (based on respiratory motion); offers long detection range and wide coverage. Disadvantages: Typically consumes more power than PIR sensors; relatively higher cost; may generate false alarms in complex environments (e.g., swaying curtains).

Millimeter-wave radar sensors operate at higher frequency bands (such as 60 GHz and 77 GHz) and represent an advanced evolution of microwave radar. Their advantages include higher resolution, enabling more precise target localization, multi-person discrimination, and even rudimentary pose recognition.

Strong anti-interference capability; effectively detects both stationary and slightly moving targets. Drawbacks: highest cost; relatively complex technology; greater challenges in power‑management. It represents the trend for high‑end smart home, security, and spatial‑analysis applications.

Ultrasonic sensor: It emits high-frequency sound waves and measures distance based on the time of the echo. When a person moves within the room, the echo pattern changes. Advantages: low cost; good penetration through non-metallic materials. Disadvantages: accuracy is easily affected by temperature and air currents;

It is susceptible to interference from other ultrasonic sources; its performance in detecting stationary targets is poor; and it has relatively high power consumption. Its applications are gradually being replaced by radar.

LiDAR: It emits laser beams to scan the environment and constructs a precise 3D point cloud using time-of-flight measurements. Advantages: extremely high accuracy, enabling precise localization and contour recognition. Disadvantages: high cost; relatively complex structure (with moving parts);

Privacy concerns (environmental scanning); it is rarely used in consumer‑grade personnel detection, being more commonly found in robot navigation and high‑precision security applications.

 

Environmental Change Sensor (Indirect Assistance):

Sound sensor (microphone): Detects specific sounds in the room—such as speech, footsteps, or coughs—to determine whether someone is present. Advantages: low cost. Disadvantages: highly susceptible to ambient noise; unable to distinguish the source of human voices; raises significant privacy concerns; cannot detect the presence of a person who remains silent.

Air quality sensors (CO2, VOC): Human respiration releases CO2 and volatile organic compounds. By monitoring significant increases in the concentrations of these gases, it is possible to infer indirectly that someone is present in the room. Advantages: capable of detecting individuals who are stationary. Disadvantages: slow response (concentration changes take time); susceptible to ventilation and external pollution sources; requires relatively complex algorithmic analysis; comparatively high cost. Typically used as a supplementary verification method.

Temperature and humidity sensor: The human body emits heat and moisture. When multiple people gather or remain in a space for an extended period, local temperature and humidity levels can rise. Advantages: low cost. Disadvantages: changes are very slow and barely noticeable; highly susceptible to environmental factors such as air conditioning, humidifiers, and weather conditions; extremely low reliability, making it virtually unsuitable as a primary sensing device.

Vision sensors (powerful but with concerns):

Camera (visible light): The most straightforward approach, identifying human bodies through image or video analysis. Advantages: Provides the richest information—counting people, tracking locations, and recognizing identities. Disadvantages: Privacy concerns are particularly acute; performance is highly dependent on lighting conditions; computational complexity is high; and costs remain relatively elevated. In typical indoor occupancy detection, its use is constrained by privacy issues.

Thermal imaging cameras detect the infrared thermal radiation emitted by the human body, generating a thermal image. Advantages: they can operate in complete darkness and do not reveal personal identity details (offering relative privacy). Disadvantages: they are expensive; their resolution is typically low; they are effective for stationary targets but are less adept at detecting subtle movements than radar.

How do you choose the “perceptual lens” that best suits you?

Prioritizing cost-effectiveness and basic functionality: PIR sensors remain a reliable choice, particularly for lighting control and simple security alarms.

The need to detect stationary and slightly moving targets calls for an enhanced user experience: microwave and millimeter-wave radar sensors have become the mainstream upgrade path for smart homes—such as smart air conditioners, occupancy‑sensing lighting, and smart bathroom devices—and for high‑end office environments, enabling true presence detection.

High-Precision Positioning and Spatial Analysis: Millimeter-wave radar or LiDAR are the preferred choices for specialized applications such as people counting and behavior analysis, though they come at a higher cost.

Privacy First: Millimeter-wave radar and thermal imaging cameras are superior to visible-light cameras, as they do not capture personally identifiable information.

Auxiliary verification: Consider integrating a CO2 sensor or an acoustic sensor to enhance the overall accuracy of the assessment.

The Future of Intelligent Spatial Perception:

Sensor fusion—such as PIR plus radar, or radar plus audio—is a key trend for enhancing detection reliability and reducing false alarms. Meanwhile, more advanced artificial intelligence algorithms are being applied to sensor data analysis, enabling more accurate, intelligent presence detection and intent prediction.

Let space become intelligent through perception, and let life be made more convenient by intelligence! Choose the right sensors and take the first step toward creating a smart environment.

Radar-based wireless human presence sensor—Xuanhengyi Technology

HE-60G millimeter-wave radar for human presence detection: 60 GHz high frequency, 3-year service life, detection range of approximately 20 square meters, IP67 protection rating, suitable for office, restroom, elevator, and library environments.