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A stud finder is a handy tool to have when hanging things up in your new home or even during construction such as when the cabinets need to be put in place. Stud finders do exactly what their name says: They find wall studs. There are three types of stud finders that use different methods to located wall beams. Once located, some of the more expensive models will even mark the location for you, while with others you will need to use a pencil.
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The magnetic stud finder is a very simple machine. It looks for the nails used in the beams to hold the drywall in place. For this reason, it doesn't always find the studs on the first pass because you might place the finder at a height on the wall that is between nails. It usually takes a few passes before a nail is found. When metal is found, the magnetic finder emits a beep letting you know it has found something. These are not as accurate due to the fact that the nail found might not be in front of the stud. In some cases, the nail could be sticking out the side of a stud holding up a cross support or some other reason such as piping, in which case when you try to nail into that location, you will still not hit a stud.
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The density sensor stud finder is extremely more accurate. It reads the density of the wall by emitting an electric field that goes through the wall and follows the sensor as you move it. The field is set to a depth that gets it past the drywall and monitors the depth of the area beyond. It notices when the wall becomes thicker, such as when it moves across a stud. It recognizes the beam because the electric field is no longer going through the wall into air, and the electrons from the field are bunching up on a more solid object. This change in flow triggers the sensor to beep in basic models, or show on a computerized panel on more expensive models.
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There are even newer models that use radar as a way of monitoring wall depth. Radar sensors work by sending out a wave that bounces back to the device, and are set to a depth that gets them past the drywall. When the sensor is over empty space, the radar travels further, in this case to the opposite wall, before bouncing back. When it it is over a stud, it hits a solid object at a closer distance, and bounces back quicker. The sensor picks up on the change in time between radar bounces and alerts the system to signal you about the change.
eHow Article: How a Stud Finder Works
