Simple magnet drywall stud finder
Take the strongest fridge magnet you’ve got and tie it on a length of string. Hold it so it hangs against the wall, then slowly slide it across. It’ll be attracted to the nails or screws that secure the wall’s wood lath or drywall to studs. Since fasteners occur at regular intervals, if you’re not finding a stud, try a bit higher or lower off the ground.