stud finders operate by picking up the disturbance in a magnetic field caused by ferrous fasteners like drywall screws screwed into studs. You can do the same with a small neodymium magnet. I wrap one in masking tape so it resembles a Hershey’s Kiss - I hold it with the small tab between my fingers and move my hand over the wall. The pull of the magnet toward a buried fastener is obvious. Once you find one fastener, it’s easy to narrow down the locations of others - vertically above/below the first one, and in a vertical line ~16” to the left or right