WiFi signals can identify you without your phone or camera

Topic: Technology

Researchers have found a way to use WiFi signals to identify people and map their surroundings. This technique works like a normal camera but uses radio waves instead of light waves. The system can even work if your own device is turned off.

WiFi signals could potentially be used to identify people and map their surroundings without relying on cameras or requiring the person being observed to carry a connected device.

Professor Thorsten Strufe from KASTEL, KIT's Institute of Information Security and Dependability, explains that by observing the propagation of radio waves, they can create an image of the surroundings and of persons who are present. This works similar to a normal camera, but instead of light waves, they use radio waves for recognition.

The technique analyzes radio waves moving through a space, so a person does not need to have a phone, smartwatch, or other WiFi enabled device with them. Even turning off your own device would not necessarily prevent the system from working. It's sufficient that other WiFi devices in your surroundings are active.

Ordinary WiFi routers could become surveillance tools, warns Julian Todt from KASTEL. The researchers say the findings reveal a potentially serious privacy risk because WiFi networks are already widespread in homes, offices, restaurants, and public spaces.

The new technique does not require specialized hardware like LIDAR sensors or CSI (channel state information). A standard WiFi device is enough. The method takes advantage of normal communications produced by legitimate users connected to a WLAN (wireless local area network).

Researchers tested the technique in a study involving 197 participants and achieved almost 100% identification accuracy, regardless of the viewing perspective or the way a person walked.

Why It Matters

This discovery raises concerns about privacy and surveillance. In India, where WiFi networks are widely available, people may unknowingly be identified and monitored without their consent.

Key Facts

• Researchers have found a way to use WiFi signals to identify people and map their surroundings with almost 100% accuracy.
• The technique works like a normal camera but uses radio waves instead of light waves.
• A standard WiFi device is enough for the system to work, and it can even function if your own device is turned off.
• Ordinary WiFi routers could become surveillance tools, posing a potentially serious privacy risk.
• The study involved 197 participants and was published in the Proceedings of the 2025 ACM SIGSAC Conference on Computer and Communications Security.

Key Terms

WLAN

A wireless local area network, essentially the WiFi network operating within a home, office, café, or similar location.

CSI

Channel state information, measurements showing how a wireless radio signal changes as it travels through an environment and reflects from walls, furniture, people, and other objects.

Implications

This discovery raises concerns about privacy and surveillance. In India, where WiFi networks are widely available, people may unknowingly be identified and monitored without their consent.