From company website: "The StudSensor™ HD25 stud finder is the perfect entry level tool for anyone looking to hang pictures, hooks, and shelves with confidence. The HD25 is easy to use and provides reliable performance for all kinds of everyday projects. Simply place the tool on the wall, press and hold the power button, and begin scanning. The HD25 detects the edges of wood and metal studs through one layer of drywall, helping you securely anchor your project into the center of the stud - where it stays"