I hate conventional stud finders. We have never been able to get one to work properly, as evidenced by the nine or so holes that are hidden behind the giant blue marlin that is hanging in the photography studio. There were another sixteen holes in the wall of our apartment where he was hanging in our living room for the same reason.
A few weeks ago I sat down with my 1994 copy of Reader's Digest Household Hints and Tips. It mentioned the use of a strong magnet to locate the studs in the walls of your house. I was skeptical but figured it had to be better than nailing hole after hole after hole hoping to hit the 2x4 on the first try.
What do you know! It actually works! You start by locating the poorly spackled nail hole in the baseboard.
Then you take your magnetic Tot Lok (any other strong magnet will work, the Tot Lok is just the one we happened to have handy) and starting at the baseboard, move your way up in a straight line, following the magnet until it is at the height you want to place your nail. You'll feel the magnet stick every few inches.
Quite ingenious, no? Too bad I didn't think of it myself, many moons ago!