Curiosity got a hold of me again. I do many handyman tasks and some times I'm in need of a stud finder and occasionally it is a cement wall, in which case its pure guess work what is behind the wall or inside the wall.
The other day I stumbled over an ad online for WALABOT, an 3D imaging sensor which lets you see what is inside a wall (for my purpose).
Simply connect to an Android telephone, calibrate and voila the display shows studs, pipes, cables and what ever else lurks inside a wall. Besides the image of the object in the wall it also displays how far away it is from the sensor - definitely useful information.
Best part - it worked flawlessly right out of the box.
The company also provides a developer kit with a myriad of possibilities for the use of this technology, but that is for another day...