Wi-Fi Turns Spy-Fi

“We are profoundly bad at asking ourselves how the things we build could be misused.”

​- Brianna Wu

​In terms of surveillance tech, Wi-Fi is having its moment. This is the fourth time in 2025 we’ve covered the growth of an invasive concept that three years ago seemed remote, even arcane: Wi-Fi sensing.

Increasingly, Wi-Fi turned Spy-Fi is ready for prime time. The Karlsruhe Institute of Technology (KIT), a German research university and think tank, found that Wi-Fi networks can use their radio signals to identify people. Any Wi-Fi network can be made to do this, no fancy hardware required. The people being identified don’t have to be logged into these networks, either. In fact, they don’t even need to carry electronic devices for this subterfuge to work; it’s enough simply to be present, minding one’s own business, within range of a given Wi-Fi router.

But given the ubiquity of Wi-Fi networks, that leaves very few places to hide. “This technology turns every router into a potential means for surveillance,” warns security/privacy expert Julian Todt of KIT. “If you regularly pass by a café that operates a Wi-Fi network, you could be identified there without noticing it and be recognized later – for example by public authorities or companies.” (Or hackers, autocrats, or foreign agents).

How does it work? By exploiting a standard feature and turning it into a vulnerability – leveraging weaknesses must be taught at Bad Actor 101 at Spy School. In this case, connected devices regularly send feedback signals to Wi-Fi routers. According to the researchers, these signals are frequently unencrypted – which means anyone nearby can capture them. Then, with the right know-how, that data can be converted into images.

Not photos exactly, but close enough – analogous to ultrasound, sonar, or radar. The more devices that are connected to a given Wi-Fi network, the fuller the picture provided – height, shape, gestures, gait, hats, purses, and more. With a little help from machine learning, our bodies turn out to be uniquely identifiable, not unlike a fingerprint.

Are there easier ways to spy on us? Most certainly – CCTV, for example. But what Wi-Fi sensing lacks in ease it makes up for in reach. As technologies go, it’s practically everywhere that humans are. The vast majority of people don’t have CCTV cameras in their homes, but they (or their neighbors) are almost guaranteed to have Wi-Fi.
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Wherever you’re reading this from, take a moment to see how many Wi-Fi networks your phone detects. If the KIT research proves correct, any one of them could be used to track your movements and determine your identity.

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