I bought a Zircon stud-finder that was touted as being able to live cable inside walls. I planned on using it to trace the crumbling armored cables insde my walls. And it wasn't cheap.
However there's so much wood joist and wood lath under the mud and plaster that the device goes bonkers.....it's completely useless even for finding a frigging joist in the wall or ceiling!!
All these things seem like they're designed for sheetrock panels like what's used in new construction suburban houses.