Stanley 77-110 Intelli-Sensor Stud Finder is a handy tool everyone should have. It easily locates the edges of studs or joists through drywall and other common wall materials. The electronic audio and visual signals are emitted once the edge of the stud is detected. It has an automatic calibration switch for easy turn-on operation, and automatic shut-off for longer battery life. It features hHigh-impact, heavy duty ABS case, with non-marring pads for wall protection, and a pencil notch for marking stud edges. Pocket size for easy storage. Requires a 9 volt battery (not included).