If your wall is hollow, check out hollow wall fixings.....they work very well, and the timber fixing can be enhanced with some instant grab adhesive.
If your luck is really in, you'll be able to fix into the timber studs behind.
I don't find stud finding electrical tools very good, which is a bit of a bore!
If you go for hollow wall fixings, get the setting tool too - it's cheap enough and saves many a headache.
John