That’s really impressive, and cool. I remember seeing a video, also from MIT I believe, where they placed a plant in a room and faced speakers towards it playing some music or sound through the speakers. A camera recorded the plant, without audio (video only), and was able to figure out what the sound was that was being played. Technological advancements like these never cease to amaze me, not only because of the impressive tech, but the innovative minds behind them that can think of things like this.
I read that when they were surveilling Bin Laden’s house they measured the vibrations on the windows to determine how many people were in there talking/walking and in which rooms.
source: Abe Davis’s Research