Here is a bit more information on how it works and the conference they will be discussing this:

In a paper accepted to the SIGGRAPH Asia conference taking place next month, the team presents a new technology called RF Capture that picks up wireless reflections off the human body to see the silhouette of a human standing behind a wall.

By tracking the silhouette, the device can trace a person’s hand as he writes in the air and even distinguish between 15 different people through a wall with nearly 90 percent accuracy.

On one hand this technology could have huge benefits.  On the other hand, it would have to be used responsibly.  Science fiction is becoming science reality.

thanks to MIT for the info