There are fancy terahertz cameras to see through walls, and X-ray scanners that can fit in the palm of your hand. Now scientists at MIT have built a way to track people with Wi-Fi signals.
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The idea is pretty simple: take two transmitters and one receiver. Each transmitter sends out a signal that is precisely 180 degrees out of phase with the other, so the two cancel each other out and the receiving antenna "hears" nothing.
But put any moving object in the area, and it reflects the signals. The signals don't cancel out, and where once there was no radio "noise" at all, there is now radio energy coming off of the moving object or person. A still object also reflects radio waves, but the time it takes for a wave to bounce back to the receiver stays the same and the reflections will still cancel out.
The invention, being developed by Dina Katabi, an electrical engineering professor, and her graduate student Fadel Adib, is called Wi-Vi. The two will present it at the Sigcomm conference in Hong Kong this August.