Electronic stud finders have never worked for me. I'm either working on a plaster and lath wall where the stud finder has no hope, the wall is textured, or there's a bunch of other junk in the wall throwing off the sensor. After wasting time, ever hopeful that it will work this once, I have always ended up just drilling holes to find studs. Good thing I'm good and Christy's great at patching plaster and drywall.
Before electronics made our lives easy, people found the nails or screws in studs with a magnet. I tested this trick out in comparison to an electronic stud finder while installing a set of shelves, and it's doubtful I'll ever use my electronic stud finder again.
Step 1: Grab Magnet From Fridge, Hang With Dental Floss
I've read that people find this method too slow, but the electronic stud finder always leaves me guessing. Once I saw the pattern of fasteners there was no question I had found studs. If you want to speed the process up, a strong and light rare-earth magnet would really seek out the nails.