The Amazing Kreskin is famous for asking that his paycheck for personal appearances be hidden, and he only allows himself to be paid if he can locate the paycheck through mental means. Kreskin has only failed to find his paycheck on a half dozen occasions, and on each of those he proceeded to read a thought in his host's mind that he agreed not to reveal in exchange for a sum equal to the fee he had forfeited.
The magician's employer writes a check for the magician's services and hides it somewhere near where the performance is to take place. As the climax to the performance, the magician puts a hand on the employer's shoulder and uses psychic vibrations to divine the check's location.
Before the performance, the magician instructs the employer to prepare and hide the check in a very specific way. The check must be sealed in an envelope, it must be hidden somewhere accessible (for example, not strapped to the belly of a homicidal wild bull), it must be within 100 yards of the performance area, the employer must know where the check is, and the check must be written on a 1" thick slab of iron.
Some of these instructions are mere smokescreens so that the employer does not guess how the effect is performed. It is the final instruction -- the one about the slab of iron -- that is the key to the effect. When the magician is ready to locate the check, a large electromagnet hidden beneath the magician's shirt is switched on, attracting the metal check. The magician talks about feeling "pulled" toward the check and simply follows the magnet's direction of attraction.