The cheapest stud finders are really nail finders, working on the assumption that the original wallboard installer put the nails in the studs.

I've also found that my "prior owner unhandy man" missed a lot of studs, but left the nails in place and hammered another on "a little bit over thataway" - sometimes a couple of times until one felt like it might have hit something (and sometimes didn't).

The "RF" finders that actually sense the stud are variable in how far they'll penetrate. Some reasonably priced ones (<$35 US) likely could find the variations through inch thick plasterboard, but others - often more expensive ones - are almost useless even on old "residential grade" stuff. Unfortunately, the only thing on the package when you go to get one is "this device is wonderful" with no actual/factual indication of what it will do, so finding the good ones (unless you know someone who has one and find one like it) is a crap shoot. From the package information, one might think they were getting a sex toy, given all the vacuous vague/promises and the low expectation of getting any actual satisfaction from using them.

John