Wi-Fi goes through walls, but it isn’t so great at getting through human bodies. Based in this piece of knowledge, a team at MIT’s Computer Science and Artificial Intelligence Lab (CSAIL) has built a detector that can see people through walls using Wi-Fi signals. It can recognize individuals and can even track the movement of their limbs with spooky accuracy.
The team’s gear comprises a sensor and an emitter that fires radio frequency (RF) signals through a wall. When the waves find a person, their body reflects some of the waves back. The reflected waves travel through the wall, where they are captured by a detector. Not every limb reflects all the Wi-Fi, all the time, so a computer stitches together images taken over time, similar to how your eye constructs patterns and letters from the bright tip of a sparkler being waved around in the dark.
The resulting images look like a lot of colored blobs, but you can clearly make out the human shape in there. A computer does even better at recognizing the people behind the wall, able to distinguish between five people with an accuracy of 95.7%.
What’s more, the system can detect movement with uncanny accuracy. In one experiment, the team had their subject use their hand to draw shapes in the air. The RF detector managed to track the shape almost as well as a Microsoft Kinect device, a machine designed to track humans in order to play video games. And the CSAIL system managed this from the next room, through a solid wall.
There are plenty of possible applications for this technology. One is clearly tracking people. You could use it as one more security layer, to recognize employees versus intruders. But the Kinect angle is the closest to the future seen by the CSAIL team. They see it being used to make movies.
Motion capture—the art of taking a persons movements and digitizing them so they can be applied to a computer-generated creature—usually means making actors wear skin-tight suits with bright dots on them so the cameras have something to track. A good RF system could do away with these costumes.
RF capture could also be used to automate your home, by say only running the heating and lights when a human is at home. Or it could call an ambulance if an elderly resident takes a fall. Or check that a baby is still breathing. Because the signals used are so weak, around 1/10,000th that of a cellphone, it should be safe to leave running all the time, making the possibilities for use almost endless.
