And here we thought the only privacy risk with having a Wi-Fi network at home was someone figuring out our password. Researchers at MIT felt that a stranger having access to your wireless network wasn't scary enough, so they developed a way for someone to use Wi-Fi signals as a sort of x-ray vision to track a person's movements in another room.

Borrowing similar techniques as used with radar and sonar, the Wi-Vi system—as the researchers have called it—sends out a pair of inverse wireless signals as pings. When they hit something stationary, they cancel each other out, but when an object is in motion it creates an offset between the signals that can be processed to determine where and how fast it's moving.

In its current state it's far from Superman's x-ray vision, though. The system isn't precise enough to determine exactly what someone is doing in another room, but that doesn't mean its useless. Using a smartphone as the signal source, Wi-Vi could provide a cheap way for rescue workers to search for captives in a building, or even as a way to hunt for survivors trapped under rubble, as long as they're moving. Or, as a mobile version of Kinect that doesn't necessarily need to see you to detect your gestures. [MIT via SlashGear]