Scientists warn this WiFi tracking method could identify you without a phone and almost nobody would notice

Researchers from the Karlsruhe Institute of Technology (KIT) have warned about a new kind of surveillance technology that can turn a WiFi router into invisible tracking tools capable of identifying people even if they are not carrying a smartphone or any connected device.

“This technology turns every router into a potential means for surveillance,” Julian Todt, one of the authors of the study warned, “If you regularly pass by a café that operates a WiFi network, you could be identified there without noticing it and be recognized later – for example by public authorities or companies.”

However, since these these feedback signals are continuously transmitted in an unencrypted format, any standard WiFi device in range can passively record them.

Researchers say that these signals can then be analysed using machine learning models to create “radio images” of people moving within the network’s range. They warn that these radio-based patterns are detailed enough to identify individuals based on how their bodies affect surrounding WiFi signals.

“By observing the propagation of radio waves, we can create an image of the surroundings and of persons who are present,” Professor Thorsten Strufe from KIT explained. “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.”

As part of the study, the researchers tested the technology on 197 participants and claimed that it was able to infer the identity of individuals with a 99.5 percent accuracy, regardless of viewing angle or walking style.

However, in order to actually link the identified people with their name and other personal details, the researchers say attackers would need other details like ping from a smartphone or a device previously associated with that individual.

They also warned that just turning off your smartphone may not protect you from being tracked.

“It’s sufficient that other WiFi devices in your surroundings are active,” Strufe added.

The paper warns that the biggest danger lies in how invisible this type of surveillance could become. Unlike CCTV cameras or facial recognition systems which are easy to spot, WiFi networks are already deeply embedded in homes, offices, cafés, airports and public spaces.

The researchers say this could eventually create what they describe as a “nearly comprehensive surveillance infrastructure” that operates quietly in the background without raising suspicion.