Image: Physics

Your WiFi router is probably sitting passively in some corner of your room, beaming out invisible light (and the internet). But it’s also sending information on all the stuff the light passes through and around. It’s essentially carrying a holographic image of the room with it.

Researchers have tried using WiFi signals to make images before, but not with an out-of-the-box commercial router, according to a release in the American Physical Society’s Physics. That’s exactly what a team of researchers at the Technical University of Munich has now done, imaging a cross in a room using an unmodified commercial Wi-Fi router.

The setup placed the cross between the router and a moving antenna, with another antenna off to the side to help with mathematical calculations. The antennae collected light directly from the router and light that reflected our bounced around and off different surfaces. Some number crunching and plotting produced an image showing the WiFi router as a bright spot, with the cross as a shadow in the foreground. Making that image 3D required combining images obtained at different distances, according to the research published this week in Physical Review Letters.

Image: Holl et al

The method has some drawbacks—it’s slow, and there’s only a set cone of light from the router inside of which accurate images can be produced, outside of which things are blurry. And the whole thing takes a long time, electronic engineer Karl Woodbridge of University College London told Physics. That issue could be fixed with more antennae. Such a system could be used for various indoor imaging purposes; Woodbridge even recommended a set of antennae attached to a “drone or truck” as a promising imaging system.

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But the researchers imply that the study should elicit a sense of worry in the reader. “Even encrypted communication transmits a three-dimensional picture of its surrounding to the outer world,” they write.

At this point, we’ve pretty much entered a reality where simply having WiFi in your house can reveal sensitive information.

No one is safe.