If you want to add an outlet to a room, you need to know how the electric runs in the walls. Punching holes in your drywall until you locate the conduit will work, but it will leave you with a mess to repair. Fortunately, by using a stud finder, you can find the electrical wires behind the drywall without creating any holes. Electric wire is placed in a metal conduit that is then run on a through the studs in the wall. As long as your stud finder has a setting for "Metal" or "Electric," you will be able to find your electrical wires.
Turn your stud finder on and switch the settings so "Electric" is selected. If you do not have a choice for "Electric," you can also use the setting for "Metal."
Place the stud finder against the wall to one side of an existing outlet or switch. Slide the stud finder around the outlet or switch until you hear a continuous beep or all the lights on your digital scale are lit (depending on the model you have). This will calibrate the stud finder for finding electrical conduit in the walls.
Slide the stud finder on the wall away from the outlet but on a path that maintains the beeping sound or keeps the lights lit. This will mean you are following the conduit. If there is any interruption to the sound or the lights begin to turn off, you have wandered off the path of the conduit. Slide the stud finder until the sound or lights return and continue.
Place a small pencil mark on the wall every 2 feet as you trace the conduit with the stud finder. This will help you remember where the conduit is behind the drywall.
Once you have located your wires and know the location of where you can install an additional switch or outlet, you must turn off the power to that room before breaking through the dry wall. Never cut or drill into a wall where you know live wires are present; you could receive a severe shock or cause a spark that can start a fire within the wall.