With a HART stud finder you have a fast easy and accurate tool you can rely on. To operate the HART Professional Stud Finder simply press and hold the button then place it on the wall and go. There is no calibration procedure. You can instantly find studs. Once you have it on the wall the LEDs show you right where the stud is. When you move the unit back and forth the HART Professional continues to track the location of the stud which makes it easy to instantly see the edges and the center of the stud. The display allows you to see the full width of objects such as single studs wires and pipes. When a live electrical wire is detected the yellow lightning bolt symbol may illuminate to indicate the presence of live wires. AAA Battery powered (not included). DO NOT USE RECHARGABLE BATTERIES. Use 1.5-volt alkaline batteries only. Package contains one stud finder.