This handy tool is designed to help you locate studs in walls, ceilings, and floors. It features a powerful sensor that can detect the presence of metal and wood studs behind drywall, plaster, and other surfaces. With its easy-to-read LCD display, you can
From Wikipedia
A stud finder is a handheld device used to locate wood or metal framing studs behind walls. In the United States, walls are typically made of drywall, though stud finders can also be used on lath and plaster walls, and in some cases, even tile.