Here is a nifty tool that lets you see through walls to find studs, pipes, and any movement. The Walabot DIY Plus can find pipes, wires, metal/wooden studs, and detect movement. It works on drywall, concrete, lath, and plaster. You will be able to see 4 inches into your walls.
The device has 3 sensing modes (panoramic, images, and expert). It works with smartphones running Android 6.0 or later.