Locates wood and metal studs up to 3/4 in behind drywall. The SpotLite pointing system in shines a beam of light on the wall to identify the target. Red LEDs light up every time a stud edge is approached. SpotLite Pointing System, an audio alert and a green LED signals when the stud edge is reached. Should scanning begin over a stud, the over-the-stud indicator alerts the user to start the scan in a new location. TruCal technology calibrates to any wall's density and a steady green LED TruCal light alerts the user. Includes 9 V Battery