You may worry that a home security camera or your laptop’s webcam could be used to spy on you, but there is another device worth watching: your WiFi router. Recent research shows the signals from ordinary WiFi routers can reveal detailed information about people nearby, and they don’t rely on cameras or microphones to do it.
Researchers in Germany discovered that common WiFi signals can be processed to create radio-based images of people and to identify individuals in seconds. You don’t need to carry a phone or any connected gadget. Simply standing within range of an active WiFi network can be enough for the technique to work.
Scientists Turned WiFi Into a Camera
A team at the Karlsruhe Institute of Technology studied how devices and routers exchange brief feedback signals to keep a wireless connection stable. Those feedback signals are not encrypted and can be measured by nearby receivers. By analyzing how the signals change when they bounce around a room, the researchers were able to reconstruct shapes and movement, essentially converting radio reflections into images.
Thorsten Strufe, one of the researchers, described the outcome as a sort of camera built from radio waves. Instead of relying on visible light, this method maps the way radio waves scatter from people and objects to form detailed silhouettes and motion patterns.
When radio waves emitted by WiFi devices reflect off a person, they create distinct patterns. The team trained machine learning models to interpret those patterns and transform them into consistent images. After a model learns a person’s unique radio-wave signature, it can recognize that individual again in just seconds, even if they change orientation or move around.
In tests with 197 volunteers, the system identified participants correctly nearly every time. The accuracy held across different body poses and walking directions, demonstrating the technique’s robustness under realistic conditions.
Does this mean you should power down your devices? Unfortunately, turning off your own phone or laptop offers little protection. The method requires only one active WiFi network in the vicinity, which describes many public and private spaces—coffee shops, offices, apartment buildings, stores, and more. Your personal devices don’t need to be transmitting for the system to detect you.
Because WiFi networks are so widespread—in homes, workplaces, and public venues—this form of identification could in theory be carried out almost anywhere without people being aware of it. The signals that routers and devices exchange are a persistent, often overlooked side channel.
There are no public reports yet of companies or governments deploying this exact technique at scale to monitor people. However, the researchers who developed the approach warn it could be adapted for mass surveillance, such as identifying protesters or tracking individuals across certain areas, particularly in countries with weak privacy safeguards. They are advocating for new WiFi standards and technical protections to limit how easily these radio-based imaging techniques can be used.
For now, practical defenses are limited. If you are within range of an active WiFi network, it is technically possible for radio-based imaging to detect your presence. The most effective long-term solutions are likely to come from updated wireless standards, improved device security, and legal privacy protections that restrict how signal data can be collected and used.