Wifi signals have become so common place that we are almost constantly surrounded in these radio frequencies. Though it provides us with the luxury of access to the internet anywhere we go,  these are exploitable to track our physical location and movement. Wifi signals are radio waves that typically float in the 2.4 to 5 giga hertz range which shine through or bounce off solid objects. This causes a distorting effect in the wifi signals which researchers have found can be exploited to  to essentially see through walls.

Professor Yanzi Zhu of University of California Santa Barbra found that just using an ordinary smartphone, it is possible to use the ambient wifi signals to track people in their homes or offices from the outside. Wifi signals are light outside of our visible spectrum which get distorted when they pass through doors or desks. This distortion in the wifi signal, while makes it difficult to discern what objects are, can be used to see specific movement of people. Humans reflect and refract wifi light as well but their movements cause discrete changes in wifi light, just as it would with light in the visible spectrum, making it easy to spot.

In order to track people, professor Zhu research team first needed to find the location of the wifi transmitter such as a router. They developed an app that utilized a smartphones built-in accelerometer and as they moved around with the phone, and gather the data on the changes in the signal strength. By calculating the numbers, they were able to discern the location of the source of the wifi light. They reported that after 4 measurements, they were able to get the location of the router with 92.6% accuracy.

With this information, they just needed to wait for movement in the wifi environment. By placing a stationary wifi measurer or detecter, it can record how the wifi light is configured with the surrounding, in a sense like a still picture. The team describes that different movement creates different changes to the wifi signal which after recording which movement make what signal change, they could figure out what movement were occurring on the other side of the walls.

They also note that with more than one wifi signal, their accuracy improves. For example, with 2 wifi routers, their accuracy increases to 99%. While there may be ways to mitigate the effect such as geofencing the building or adding more noise to the wifi environment, these seem to have limited effectiveness. The simplicity of the detection method would mean that it would be easy for a peeping tom to spy as they would only need to carry around a phone, or worse for potential burglar who would require as little equipment as possible to be unsuspicious. It feels that fight for privacy may start to become more difficult.