The stud detector uses electronic signals to locate the exact position of studs or joists through dry wall and other common wall materials.once the edge of a stud bas been detected,the detector unit emits audio and visual signals (led display) that allow you to pinpoint its center position.the leds will light and beep sounds,whenever the detector detects stud.size:138x70x28(mm)weight:150g(including a 9v battery)