Do you really wish you had X-ray vision? Sure, it would be fun to see what your neighbors are doing behind those walls — until you see something you wish you hadn’t.

Regardless, researchers at MIT have developed a sensing technology that uses low-power Wi-Fi to detect moving people. It follows other wall-penetrating sensor tech using radar and heavy equipment.

The Wi-Vi system by Dina Katabi and Fadel Adib sends out a low-power Wi-Fi signal and tracks its reflections to sense people moving around, even if they’re in closed rooms or behind walls.

Part of a Wi-Fi signal transmitted at a wall will penetrate it and reflect off people on the other side. The MIT system ignores all the other reflects, such as from objects, to focus on those from moving people only. It can determine the number of moving people in the room and their relative locations.

The system sends out two nearly identical signals, but one is the inverse of the other, and thus they cancel each other out.

“So, if the person moves behind the wall, all reflections from static objects are cancelled out, and the only thing registered by the device is the moving human,” Adib, a graduate student in MIT’s Department of Electrical Engineering and Computer Science, was quoted as saying in a release.

The Wi-Vi receiver uses changes in the signal reflection time to calculate where a moving person is behind a wall. It can also detect gestures such as arm waving and could be used to control home lighting or appliances in another room. It could also let people communicate with the outside using hand signals alone.

British researchers have also been investigating how to use Wi-Fi for surveillance and urban warfare, but the MIT system could be used in applications such as search and rescue, law enforcement, or personal security.

“If you are walking at night and you have the feeling that someone is following you, then you could use it to check if there is someone behind the fence or behind a corner,” said Katabi, a professor in the department.

Or the NSA could use it to see how badly you dance in front of your mirror.

The research (PDF) will be shown at the Sigcomm conference in Hong Kong in August. Check out a brief demo in the vid below.