We took the acclaimed Stud Sensor & upgraded it with our innovative Spot Lite Pointing System The Stud Sensor SL stud finder is the 21st century incarnation of the original stud finder that Zircon introduced to the world in 1980 Powered by proprietary technology it finds the edges of wood & metal studs & features Zircons patented Spot Lite Pointing System Its the sure way to securely hang pictures shelves mirrors & more Locates the edge of wood or metal studs behind drywall up to 19 mm thick A red LED lights up every time a stud edge is approached The patented Spot Lite Pointing System & green LED signals when the stud edge is reached Should scanning begin over a stud Zircons patented overthestud indicator alerts the user to start the scan in a new location Patented Tru Cal technology calibrates to any walls density & a green LED Tru Cal light alerts the user when the tool is calibrated & ready to scan