The Action Lab set up an interesting proof of concept using a smartphone plus a cheap radio frequency 3D imaging doo-dad to sense motion in another room.
He demonstrates it with a Walabot, which runs about $80. This is different than some other stud finder apps, but operates on many of the same principles. It's also different than consumer-grade FLIR devices that are helpful for checking buildings for heat loss and so on.
• How To Use Your Smartphone to See Through Walls! Superman's X-ray Vision Challenge (YTouTube / The Action Lab)
