Wi-Fi Networks Can Identify People Without Cameras, Study Finds

The technique relies on beamforming feedback information, a type of signal that connected devices routinely send back to a router. This information is transmitted without encryption, meaning anyone within range of the network could potentially intercept and read it. By analyzing these radio signals over time, the system builds images of people from multiple viewpoints inside a space.

Earlier wireless sensing methods often required specialized equipment, such as LIDAR sensors or detailed measurements of channel state information. By contrast, the researchers say a standard, unmodified Wi-Fi device is entirely sufficient to carry out this new identification process. A user does not need to carry a phone, smartwatch, or other Wi-Fi-enabled device for the system to work. Turning off one's own device would not prevent identification, since other active Wi-Fi devices nearby could still be used.

Professor Thorsten Strufe of KASTEL said, "By observing the propagation of radio waves, we can create an image of the surroundings and of persons who are present. This works similar to a normal camera, the difference being that in our case, radio waves instead of light waves are used for the recognition."

The researchers argue that widespread wireless networks could create privacy concerns because they operate throughout homes, offices, restaurants, cafés, and other public environments. Felix Morsbach noted that compared with existing surveillance options, such as CCTV footage or connected video doorbells, wireless signals leave no visible trace behind. "The omnipresent wireless networks might become a nearly comprehensive surveillance infrastructure with one concerning property: they are invisible and raise no suspicion," Morsbach added.

Professor Strufe cautioned that this invisibility could make the technology particularly attractive within certain authoritarian political systems around the world. "The technology is powerful, but at the same time entails risks to our fundamental rights, especially to privacy," he said. Therefore, widespread deployment could make individual encounters difficult to distinguish from ordinary wireless activity.

The researchers argue that privacy safeguards should be incorporated into Wi-Fi technology before such capabilities become widely and easily exploited. Specifically, they are calling for protections to be written into the forthcoming IEEE 802.11bf wireless standard currently under active development. The study was originally reported by ScienceDaily and covered by TechRadar.