I wanted to install a shelving system into my closet. The stud finder seems to detect live wires over a large area (approximately 4 by 4 feet!) The closet is in the basement, with no power outlets except the light fixture. But the stud finder's signal turns on about 3 feet above ground and continues all the way to the ceiling. I checked it with two different stud finders (same result). Question: is this even possible??? That there is so much going on behind a closet wall? I don't want to drill through any wires, but honestly, a closet like this, without shelves is quite useless...
Here is an easy method to determine the location of live wires, with a stud finder. I have a stud finder on which there is no means to adjust the sensitivity of the live wire detector. However, you may use paper for the same purpose. Stud finder is sensitive to the electric field; electric field depends on the distance (i.e. how far you are from the live wire) and the medium (i.e. the material between you and wire (air or other material). If you put some paper between the stud finder and the wall you decrease the sensitivity of the stud finder. I use phone book pages for this purpose (they are free and you may add as many pages as needed). The thickness of the pages may go from one page to 1 centimeter or more depending on the current in the wire, and the paint used on the wall. You will see that the stud finder sounds for electricity only when it comes on top of the wire; you can pinpoint the location of the wire exactly. I hope this info helps someone. Good luck.
With most live wire detectors there is an adjustment wheel that sets the sensitivity. If you have this turned up too high it won't give a localised reading.
Usual procedure is to turn the device on, then in free air, adjust the sensitivity up until the detector emits a tone, then turn back until it turns off.
Sensitivity may be affected by metalwork on the other side of the plasterboard/drywall. So you may need to back off the sensitivity further.
Test the detector somewhere else. For example if you have a power outlet and know the cables run vertically from that outlet, use that area to adjust the sensitivity to give a good localised indication of the wire run. Then try it in your closet.
If you have un-insulated hollow interior walls ("stud walls") and can justify buying, renting or borrowing an inspection camera, you may be able to make a small hole in a "safe" area and use that to locate wooden studs.
It's best to do a visible inspection. Just cut a small hole at the level of a normal power outlet and use a flash light and mirror to look up in the cavity wall. After the inspection, either patch the wall/paint or just install a blank plate over the hole. If you don't have a mirror, a camera phone with a flash works pretty well.
The live wire detectors can give false positives with no wires in the area. I use tic testers all the time and when close to any on my 3 high voltage transformers they will go nuts for a large area. To find the stud when the detector is giving false info turn off the circuit or circuits that may have wires running in the wall, now find the stud and mark both sides or the left and right so you know the stud location. When using screws to install shelf hardware use 1-1/4" or shorter screws and this will allow clearance of the wallboard / plaster as the wires are required to be 1-1/4" from the face of the stud. Using this method the screw will be centered in the stud so of the wire is filling down the side of the board the wires will be fine. I have used this method for many years and never hit a wire that was installed to code.