I bought this thing specifically to find ceiling joists to securely fasten the joist over the ridge of the cathedral ceiling. The roof/ceiling is framed with trusses on about 24" centers, and I know where they are, but I didn't want to poke a bunch of holes to find each one. No luck with this thing - it's no better than my circa 1980 Sears Craftsman. What actually worked was using a stack of neodymium magnets to find drywall screws and then drilling holes to mark the position of something solid over to confirm the ceiling. A stack of magnets is a lot cheaper, so don't waste your money on that. Trick.
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