Review on Enhanced 5 in 1 Stud Finder Wall Scanner - Ultimate Wood Beam, Drywall, Joist, Pipe, AC Wire and Metal Studs Locator with LCD Display - Best Electronic Wall Detector for Precise Edge and Center Finding by Michael Harden

For 15 years I've been dealing with old houses with plaster/grid walls, even drywall over plaster and battens, with my old Stanley shelf finder. Stanley only works with 1/2 inch thick drywall - almost useless with anything heavier. Merece works great with 1/2" drywall - very accurate. There's still some guesswork with the plaster and splint, but it still defines the posts to within 1/2" or so. (Tip: move at heavier walls slowly and take multiple measurements. Make marks on the wall for each pass; averaging multiple passes is slightly more accurate than a single measurement.) The pipe and wire functions work even better Pull this thing out before you get into the wall and check it out, even if you're pretty sure your house doesn't have any wiring or plumbing.