Stud finder

A stud finder is a tool for finding hidden structural components in a wall or ceiling, such as studs, joists, and stringers. Some stud finders are also able to locate hidden engineering assets, such as pipes and electrical wiring.

Mechanism
Stud finders find studs by either of two methods. Simple, manual stud finders employ a magnetic indicator, which is attracted to the iron in common nails. Since nails are only likely to appear in structural members (holding the members together or binding the wall material (e.g. Sheetrock) to the members) the nails are a reasonable proxy for studs. Manual stud finders may interpret iron piping as studs, due to their magnetic attraction.

Electronic stud finders sense the density of a wall, interpreting higher density locations as studs. High-end electronic stud finders can be set to at normal or extra depth, for metal items, and for live A/C current.

Purpose
Many jobs require the successful location and identification of studs or engineering assets. Carpenters may anchor shelving in the wall's studs, for instance. When adding an electrical outlet, electricians may need to find electrical wiring to tap into, and a stud to attach the electrical box to. During renovations, workers may want to avoid hidden electrical and plumbing assets as they cut into walls.