The old-fashioned way of finding a stud to drill or nail into---by tapping on the wall until you hear a "solid" sound---is haphazard at best. At worst, it can result in damaged sheet rock from missing the stud with the drill or nail. The Ryobi EST0002 StudTech stud finder locates wood and metal studs electronically by sensing differences in the wall's density. The StudTech can read to a depth of 3/4-inch and also detects joists behind ceilings and floors.
Calibrate the instrument to the density of the wall material by placing it flat against the wall and holding down the On/Off button on the left side for four seconds.
Turn the StudTech on and slide it horizontally along the wall until the red LED lights and a beep sounds. Make a mark in line with the center of the stud finder. This is one edge of the stud.
Continue sliding the stud finder in the same direction until the LED turns off. Stop, then slide the unit in the opposite direction until the LED lights and beep sounds again. Mark this spot as the other edge of the stud.
Mark the middle of the stud, centered between the first two marks. Nail or drill into in the center, the strongest point.
Recalibrate the StudTech in a different place on the wall and start over if the lights blink and the beep sounds repeatedly. This indicates that your first calibration was over a stud and not a hollow space.