What is "stud finder"

n. a small permanent magnet in a metal container; when the magnet clicks against the container it indicates that the magnet is directly over an iron nail that holds the wallboard to a stud

A stud finder (also stud detector or stud sensor) is a handheld device used to locate framing studs located behind the final walling surface, usually drywall. While there are many different stud finders available, they all fall into two main categories, magnetic stud detectors and electric stud finders.