What is Wi-Fi sensing?
A plain-language guide to sensing a room through its Wi-Fi: how it works, what it can and cannot detect, how it compares with cameras and radar, and what the new Wi-Fi sensing standard changes.
Published by Stillsense · Sources reviewed
Wi-Fi sensing in one paragraph
Wi-Fi sensing is the use of ordinary Wi-Fi radio signals to detect what is happening in a space, such as presence, movement and, at rest, breathing. It needs no camera, no microphone and nothing worn. It works because people change the way radio waves travel through a room, and a Wi-Fi receiver can measure that change. The same idea is also called WLAN sensing, and it is now covered by an IEEE standard, 802.11bf.
How Wi-Fi sensing works
Wi-Fi signals do not travel in a straight line from one device to another. They bounce off walls, furniture and people, and reach the receiver along many paths at once. Every Wi-Fi receiver already measures the combined effect of those paths so that it can decode data. That measurement is called Channel State Information (CSI): the strength and timing of the signal on each of the narrow frequency slices a Wi-Fi channel is divided into.
When someone walks across the room, sits down or breathes, the paths change and so does the CSI. Wi-Fi sensing reads that stream of measurements and uses signal processing and machine learning to recognise patterns: an empty room, a person moving, someone leaving a bed, a sudden change followed by stillness.
No image is formed at any point. The raw material is a series of numbers describing a radio channel, not a picture or a sound recording.
What Wi-Fi sensing can detect
The larger and more distinct the movement, the easier it is to detect dependably. Roughly in order of difficulty:
- Presence and occupancy: whether someone is in a space, including when they sit still.
- Motion: that someone is moving, and how much.
- Events: patterns such as leaving a bed, or a fall followed by no movement.
- Breathing rate: the small, regular chest movement of a person at rest or asleep.
- Heart rate: the hardest of these, because the movement is very small.
IEEE 802.11bf: Wi-Fi sensing as a standard
For most of its history, Wi-Fi sensing relied on vendor-specific ways of getting CSI out of a chipset. IEEE 802.11bf changes that. The amendment was approved by the IEEE Standards Association on 28 May 2025 and published on 26 September 2025. It defines how Wi-Fi devices set up and carry out sensing measurements with each other, in the licence-exempt bands between 1 and 7.125 GHz (which include the familiar 2.4, 5 and 6 GHz) and above 45 GHz.
The standard describes the measurement procedure. It does not define applications, and it says nothing about how accurate any product is. What it gives chipmakers, router vendors and platforms is a shared way to build sensing into ordinary Wi-Fi hardware.
What Wi-Fi sensing cannot do
Wi-Fi sensing is not a camera with the lens removed, and it helps to be exact about its limits.
- It does not produce images, and it does not recognise faces or identify who a person is.
- It does not give detailed body posture or pose.
- Results depend on the space. Layout, wall materials, moved furniture, pets and fans all affect the signal.
- Telling several people apart in the same room is hard.
- A result from a lab does not transfer automatically to a lived-in home. Each capability has to be shown to work in the setting where it will be used.
Privacy
Wi-Fi sensing captures no image and no sound, which is why it is considered for bedrooms and bathrooms where a camera would not be acceptable. That does not make the output anonymous. Information about when a person is home, asleep or moving is personal data, and it needs the same care over access, retention and consent as any other.
Where the processing happens matters. Stillsense interprets the signal on a device in the home, so the raw signal does not leave the room.
How Stillsense handles privacy and evidenceHow Stillsense uses Wi-Fi sensing
Stillsense pairs a small sensor with the Wi-Fi already in a building and reads the signal continuously. The interpretation runs on the device. In care settings it is used to notice presence, movement, bed-exits and falls; in the home, to give lighting, heating and automations a dependable sense of whether someone is there.
We label every capability with its real maturity rather than a single headline claim, and we publish the list.
See how Stillsense works, step by stepWi-Fi sensing compared with other ways to sense a room
These rows describe how each approach works in general. They are not a performance benchmark, and the right choice depends on the setting.
| Approach | What it captures | What it needs | Typical limit |
|---|---|---|---|
| Wi-Fi sensing | Changes in Wi-Fi radio signals. No image, no sound. | Wi-Fi in the space, plus hardware and software that can read the signal. | Sensitive to layout and changes in the room; accuracy has to be shown per setting. |
| Camera | Images or video, sometimes anonymised or infrared. | A camera with a clear view in each room. | Intrusive in private rooms; sees only what is in its field of view. |
| Passive infrared (PIR) | Moving body heat within a zone. | A sensor in each room or zone. | Loses track of a person who is sitting or lying still. |
| mmWave radar | Reflected radar signals. No image, no sound. | A dedicated radar unit, typically mounted in each room. | Range and line-of-sight limits; one more device to install per room. |
| Wearable or pendant alarm | Movement of the wearer, or a button press. | To be worn, charged and, for a button, pressed. | Works only while it is worn. |
Common questions about Wi-Fi sensing
- Does Wi-Fi sensing use cameras?
- No. Wi-Fi sensing measures how radio signals change as they cross a room. There is no lens and no microphone, and no image or sound is recorded.
- Can Wi-Fi sensing see through walls?
- Wi-Fi signals pass through most interior walls, so sensing is not limited to a direct line of sight the way a camera is. It still does not "see" in the visual sense: it detects that something is moving and how, not what it looks like. How far coverage reaches depends on the building.
- What is IEEE 802.11bf?
- It is the amendment to the Wi-Fi standard that covers sensing, also called WLAN sensing. It was approved in May 2025 and published in September 2025. It defines how devices perform sensing measurements, not what applications do with them.
- Is Wi-Fi sensing accurate enough for fall detection?
- That has to be answered product by product and setting by setting, with missed events and false alerts measured under real conditions. Stillsense offers fall detection, but independent validation is planned and not yet underway, so we do not present it as a safety-grade guarantee.
- Is data from Wi-Fi sensing personal data?
- Yes, when it can be linked to a person or a household. It contains no image or sound, but patterns of presence and activity are still personal data and should be handled that way.
Sources and method
This guide is written by Stillsense, a company that builds Wi-Fi sensing products. The description of the standard is based on the IEEE sources below, reviewed on the date shown. General descriptions of sensing approaches are not performance claims about any product. Statements about Stillsense reflect our product documentation and current testing status.