The stanley intelli tools stud sensor 300 uses onepass centre find technology to locate edges of studs joists or live ac wires through drywall or other common building materials once the edge of the stud has been detected the stud sensor 300 displays red leds and sounds an audible tone a v shaped marking channel with an led allows accurate marking the stud sensor 300 can perform a deep metal scan of up to 75mm 3 inch it has a backlit lcd screen which is ideal for low light conditions