Here is a goal: How to find studs in a wall

How would you accomplish this goal?

Select from the following. +Move a beer can along a wall, when the can clings to the wall, its found a nail and you have found a stud.; +Move a magnet along a wall, when the magnet clings to the wall, its found a nail and you have found a stud.;
Move a magnet along a wall, when the magnet clings to the wall, its found a nail and you have found a stud.