MIT researchers used Wi-Fi to recognize people through walls

Paper: http://rfcapture.csail.mit.edu/rfcapture-paper.pdf (site is currently slow)

It doesn't use an unmodified wifi base station, of course. Squinting at their photos, it looks like it uses at least 16 antennas. It's basically a big 5-7ghz phased array radar. If it's got 16 radios connected to those 16 antennas, then it probably costs at least a thousand bucks.

It doesn't use wifi hardware, it doesn't use wifi transmission codes, it doesn't use wifi frequencies. It has nothing to do with wifi.