As the name suggests a stud finder detects studs behind the surface of a wall. Light Indicator and Audio Alarm: ST100B stud finder is equipped with 4 level-flash-light, light up every time a stud edge is approached or be located, in the meanwhile, the beeping will let you know you stop move once you find the edge of wood or metal behind the wall Affordable and Accuracy: No more modes you need to learn, just keep it simple. Holding the button, it beeps right away for 2 seconds (it's calibrating), hold it over a non-stud area. When it's done, now you can slide it around to detect (keep holding button) until you find the edge of a stud Why You Need eOUTIL Stud Finder: eOUTIL stud detector quickly locates wood, metal and joist hidden in the walls, floors and ceilings of the house. It can work on different wall surfaces, such as lath, wallpaper wood flooring, acoustic ceiling, painted walls, etc. helping you avoid danger when installing TVs, cabinets, garage racks, etc. 3/4 Inches Deep Detection for Wood and Metal Electrical stud finder: eOUTIL stud finders actively detect differences in wall density to find studs. It uses with a 9v 6F22 battery (Not included) as a power source Specification: 5.5 x 2.9 x 1.2 inches; 3.6 oz weight