The KASTEL Institute at the Karlsruhe Institute of Technology (KIT) has presented a system capable of identifying people inside a room without a single camera and without any special sensors. The approach is based on analyzing ordinary radio signals from wireless Wi-Fi networks. An experiment involving 197 volunteers demonstrated recognition accuracy of nearly 100 percent, with the result independent of both the angle at which the person was located and whether they were moving at the time of observation.
How Wi-Fi Became an Invisible Camera
According to the lead researcher, Professor Thorsten Strufe, by observing the propagation of radio waves, the system is able to construct an image of the surrounding environment and the people present in it. “It works similarly to an ordinary camera; the only difference is that in our case, identification uses not light but ordinary radio waves,” the scientist explained. Thus, a familiar wireless network becomes a tool for visualizing space, requiring no optical sensors.
Working Principle: Feedback Signals
The technology relies on feedback signals that client devices connected to the network send to the router. The key point: this information is transmitted without encryption, meaning that any participant within the network's coverage area can theoretically intercept and read it. By analyzing these radio signals over time, the researchers learned to reconstruct images of people from different viewpoints inside a room. Moreover, no special equipment is required — standard, unmodified Wi-Fi devices are sufficient.
Experiment Results: 197 Volunteers
During testing, the system was evaluated on 197 volunteers and showed nearly complete identification accuracy. The method proved robust to changes in scene geometry: the viewing angle and the person's motion state (static or moving) did not reduce the result. This makes the technology potentially applicable in a wide range of real-world conditions — from a residential room to an open office space.
Why Turning Off a Device Won't Help
An important property of the approach: a person does not need to carry a smartphone, smartwatch, or any other device with a Wi-Fi module. If such a device is present, turning it off does not protect against surveillance — the system works on the signals emitted by the other connected devices within the coverage area. This fundamentally distinguishes the threat from familiar scenarios where simply switching off a personal gadget is enough.
Privacy Threat and Invisible Surveillance
Wireless networks are ubiquitous: they are present in homes, offices, restaurants, cafés, and other public places, creating a systemic threat to privacy. Traditionally, intelligence agencies and cybercriminals conduct surveillance by tapping into video surveillance systems and video doorbell cameras. However, wireless networks have an important advantage for the observer — they are invisible and raise no suspicion, since they are perceived by those around as ordinary infrastructure.
Protection: The IEEE 802.11bf Standard
To protect people from such invisible surveillance, the researchers propose embedding privacy safeguards directly into the technology at the standard level. In particular, a version of the IEEE 802.11bf standard is currently being developed to address privacy concerns in the operation of wireless networks. The formation of such normative mechanisms could become a key barrier against the mass abuse of the ability to visualize people from radio signals.
