Shelly Launches Millimeter-Wave Radar Sensor: Detects 10 People Simultaneously Without a Camera

Smart home brand Shelly, following the launch of its $50 subscription-free security camera, has released another automation accessory—the Shelly Presence Gen4 sensor. This device uses millimeter-wave radar technology rather than a camera, allowing it to track the movement of multiple people within a room or large space without recording any images.

Camera-Free Presence Detection: How Millimeter-Wave Radar Works

The core of the Shelly Presence Gen4 is a millimeter-wave radar chip. Unlike ordinary PIR (passive infrared) sensors that can only detect large movements, millimeter-wave radar can capture micro-movements, such as the rise and fall of the chest during breathing. This means that even when a person is sitting still, the sensor can determine their presence.

The company claims the sensor can detect up to 10 people simultaneously. This capability has clear significance in smart home scenarios: traditional sensors typically output only a binary "occupied/unoccupied" signal, whereas the Gen4 can provide more granular information about the number of people and their positions, enabling smarter automation rules—such as adjusting air conditioning airflow or lighting brightness based on the number of people in a room.

Because it does not rely on a camera, the Shelly Presence Gen4 sidesteps privacy concerns. It does not capture or store any images, analyzing the environment solely through radio wave reflections. For private spaces such as bedrooms and bathrooms, this approach is more acceptable than cameras.

Millimeter-wave radar typically refers to radar systems operating in the 30GHz to 300GHz frequency band (corresponding to wavelengths of 1mm to 10mm). In consumer-grade presence sensors, commonly used frequency bands are 24GHz, 60GHz, and 77GHz. The core principle is to transmit frequency-modulated continuous wave (FMCW) and receive echoes reflected from targets. By analyzing the frequency difference and phase changes between the echo and the transmitted signal, the target's distance, velocity, and angle information can be calculated. Unlike cameras, millimeter-wave radar does not depend on visible light, so it can operate in complete darkness, smoke, or strong light environments, while not capturing any identifiable biometric images. Compared to traditional PIR (passive infrared) sensors that can only perceive movement caused by temperature changes, millimeter-wave radar is sensitive enough to detect sub-millimeter micro-movements such as breathing and heartbeat, which is the key to its ability to determine whether a stationary person is present.

PIR (passive infrared) sensors are the most common presence detection components in traditional security and automatic lighting. They sense changes in infrared radiation within the field of view through pyroelectric materials. When a human body (heat source) moves within the detection zone, the infrared radiation distribution changes, triggering a signal. PIR's fatal weakness is that it can only detect "moving heat sources." Once a person sits still or falls asleep, the infrared radiation distribution no longer changes, and the sensor determines "no one present," causing lights to turn off or air conditioning to shut down. Additionally, PIR cannot provide people counting or location information—it can only output an on/off signal. Millimeter-wave radar, by continuously transmitting and receiving radio waves, can extract presence signals from subtle chest movements even when the target is completely still, thereby compensating for this PIR deficiency.

Integration with the Shelly Ecosystem and Market Positioning

In recent years, Shelly has attracted users in the smart home space with a "no subscription, local-first" strategy. The $50 security camera launched last month also emphasized no monthly fees, and the Presence Gen4 continues this approach.

The sensor can connect to Shelly's existing automation system, linking with lights, air conditioning, security, and other devices. For example, when more than 3 people are detected in the living room, lights automatically brighten; when everyone leaves, appliances automatically turn off. For users already using Shelly relays, the Gen4 can complement fine-grained presence detection capabilities.

Shelly has not yet announced the specific price or release date for the Gen4. However, given its camera product pricing strategy, the Gen4 will likely remain under $100 to stay competitive.

Privacy and Precision: The Trade-offs of Millimeter-Wave Radar

The privacy advantages of millimeter-wave radar are obvious, but its precision is also limited by physical characteristics. Radar waves can penetrate certain non-metallic materials, but metal and thick walls will block signals. This means sensor installation positions need to be carefully planned, otherwise detection blind spots may occur.

Additionally, the ability to detect 10 people simultaneously may be limited by space size and people distribution in actual home environments. If multiple people stand closely together, radar reflection signals may overlap, causing counting errors. Shelly has not published specific detection accuracy data, and actual performance remains to be verified through testing.

Compared to camera-based solutions, millimeter-wave radar cannot provide identity recognition or facial information—it can only determine "how many people" and "whether they are moving." For scenarios requiring distinction between family members and strangers, other sensors are still needed.

Multi-target tracking is another significant advantage of millimeter-wave radar over PIR, but its technical implementation has clear boundaries. Radar distinguishes different targets through three-dimensional information of range-Doppler-angle, and in theory can track multiple reflection points simultaneously. However, when multiple people are close together or within the same angular resolution cell, echo signals will alias, causing counting errors. Additionally, radar can produce reflections from metal objects, ceiling fans, moving curtains, etc., potentially causing false alarms. In actual home environments, room size, furniture layout, installation height, and angle all significantly affect detection accuracy. Shelly has not published parameters such as the Gen4's angular resolution, detection range, and minimum resolvable spacing, so its "up to 10 people" claim should be understood as an upper limit under ideal conditions, not a guarantee in any scenario.

GDPR (General Data Protection Regulation) is a privacy regulation that took effect in the EU in 2018, setting strict restrictions on the collection and processing of biometric data. Camera-based solutions easily cross the line in smart homes, because if captured images can be used to identify individuals, they constitute biometric data, requiring explicit consent and compliance with the minimization principle. Millimeter-wave radar does not generate images and does not collect facial or gait information that can directly identify individuals, so it is typically not classified as biometric data processing. This gives camera-free sensors a natural advantage in privacy compliance, especially suitable for sensitive scenarios such as bedrooms, bathrooms, and nursing homes. However, note that if radar data is used to infer health status (such as breathing rate), it may still be considered sensitive data in certain jurisdictions, and manufacturers must clearly explain this in their privacy policies.

Impact on the Smart Home Industry

The launch of the Shelly Presence Gen4 reflects a trend in smart home sensors: evolving from simple infrared sensing toward higher-precision radar perception. The declining cost of millimeter-wave radar is enabling consumer-grade products to integrate multi-target tracking capabilities.

That said, privacy compliance pressure is also driving camera-free solutions. Regulations such as the EU's GDPR impose strict restrictions on biometric data, and millimeter-wave radar does not involve personal image data, making it easier to pass compliance reviews.

If the Gen4 is priced reasonably, it could become a high-volume accessory in the Shelly ecosystem and stimulate other manufacturers to follow suit. But whether it ultimately wins the market depends on the balance between actual detection accuracy, installation convenience, and price.