"Non-line-of-sight imaging" is the technique of shining light in a direction and measuring all the ways it bounces off objects to determine their rough shape — including ones the person holding the camera can't see. That means that, historically, they've been able to use NLOS imaging to, say, detect an object hidden around a corner in a hallway.
Now some Stanford researchers have refined NLOS to do a new trick: They shine the laser through a keyhole and get back enough information to infer the rough shape of objects all throughout the room.
The research could one day provide a way for police or the military to assess the risks of entering a room before actually breaking down the door and storming their way inside, using nothing but a small crack in the wall or a gap around a window or doorway. The new technique could also provide new techniques for autonomous navigation systems to spot hidden hazards long before they become a threat in situations where the previous NLOS techniques weren't practical given the environment.
So, it's both technically fascinating and totally creepy, two elements that seem present in a surprising amount of engineering innovations these days.