Start with simple methods for finding the studs behind panelling before resorting to an electronic stud finder. Expensive systems require some training to operate correctly, and are never foolproof. Using the best stud finder can yield confusing results--having a backup method always makes good sense. Extra features like centre marking and AC current detection can save time and avoid trouble.
For occasional use, such as locating a solid spot to hang a heavy picture frame, try magnets first. A strong magnet could pull strongly enough to tug noticeably in your grip, or even stick to the head of the hidden nail. For a more sensitive reading, suspend a small magnet from a string and move it along the surface of the wall both up and down. Wherever it deflects towards the wall, make a small mark. A vertical row of marks locates the nails already in the centre of the stud.
Electronic stud finders find the stud itself, and not the metal fasteners embedded in it. Most use a simple sonar system, transmitting a sonic pulse through the panelling and reading the echo. If the echo comes almost immediately, the reflecting surface is close and the detector lights up to signal that a stud has been found. Many stud finders are set to read positive at a depth of no more than 1 1/2 inches. Individual devices will vary--some have two depth settings. Remember that the device is telling you that it sees something that's within that range. What it sees is not always a stud. Take readings at various heights on the wall and make sure they mark a vertical line that indicates a stud. Sonar stud finders don't turn on immediately--some take several seconds to initialise, and if taken off the wall and replaced, they will give a false reading. Echoes can also be a problem--hold the device with one hand on the correct gripping points and keep your other hand out of the way. Wall materials offer different levels of resistance to sonic pulses--to sonar, drywall looks more transparent than Formica. Since floors are built of several layers of different materials, stud sensors often fail to find joists.
Simple stud finders often get high ratings in comparison studies. Simplified functions and displays make practical use easier. The range of sonar stud finders rarely exceeds 1 1/2 inches despite the price of the device. More expensive stud finders can detect conduits, pipes and electrical wiring as well as studs. Devices that automatically indicate which of these is detected are easier to understand than those with a variety of manually-set functions. In a manually-set unit, a green light on one function setting could indicate AC wiring in the wall, while on a different setting, it may indicate the edge of a stud.