Researchers in Germany are warning that ordinary WiFi routers could be used as a form of invisible surveillance capable of identifying people with near-perfect accuracy.

A team from the Karlsruhe Institute of Technology (KIT) developed a system called “BFId” that uses beamforming feedback information (BFI) and machine learning to identify individuals moving within range of a wireless network.

Beamforming, introduced with WiFi 5 technology, helps routers direct wireless signals more efficiently toward connected devices. To function, connected devices send feedback data to routers about signal quality and positioning.

Unlike earlier systems that relied on expensive sensors or specialized equipment, the new method works with ordinary WiFi hardware already present in most homes and businesses. 

According to the researchers, the method achieved 99.5% accuracy during testing involving 197 participants.

“By observing how radio waves spread, we can create an image of the surroundings and of the people present,” said Professor Thorsten Strufe from KIT’s Institute of Information Security and Dependability in a press release. 

“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 cybersecurity expert explained. “Thus, it does not matter whether you carry a WiFi device on you or not.”

The researchers said turning off a smartphone is not enough to avoid detection because nearby wireless devices connected to the network can still generate sufficient signal activity for the system to function.

The team warned that the technology could transform everyday routers into quiet monitoring systems.

“This technology turns every router into a potential means for surveillance,” warns researcher Julian Todt. “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.”

“The omnipresent wireless networks might become a nearly comprehensive surveillance infrastructure with one concerning property: they are invisible and raise no suspicion,” Researcher Felix Morsbach said. 

The researchers also expressed concern that the technology could be used by authoritarian governments to monitor protesters or track citizens without their knowledge. “The technology is powerful, but at the same time entails risks to our fundamental rights, especially to privacy,” Professor Strufe said.

Amid privacy concerns, researchers are urging stronger protections and safeguards to be included in the upcoming IEEE 802.11bf WiFi standard.

Approved in 2024, IEEE 802.11bf, also known as the WiFi Sensing standard, creates a framework that allows WiFi devices to detect environmental changes by analyzing variations in radio signals.