From the Manufacturer

Black & Decker Stud Sensor takes the guesswork out of locating wood studs to hang pictures, install closet shelving, run chair railing and more. Whether you are a pro, do-it-yourselfer or decorator, this Stud Sensor will help you get the job done faster and easier. Stud Sensors detect studs through walls by sensing the differences in wall density between studs and the hollow spaces in your walls. This Stud Sensor has both audible and visual indicators that show when the edge of a stud is located. It is always best to hang shelves, photographs, artwork and other items securely into the studs in your walls. If these items are secured only in the drywall, nails and anchors can come loose under their own weight over time. With the diameter of a stud being less than 1-inch thick and studs being placed either every 16 inches or 24 inches, depending on the construction of your home, it isnt always easy to guesstimate a studs location. Without a stud sensor you can only guess where studs may be hidden under your walls. This usually results in driving a nail or anchor between the studs in the empty spaces in your walls, leaving holes.