One of the cleanest versions of this type of effect – not sure if this was the very first of its type but it certainly seems to be what Collectors’ Workshop’s Hemingway Lock and Bob Solari’s Pandora’s Lox version were based upon.
You show the padlock and how only one key opens the padlock. Lock the padlock and hand all five keys to the spectator. They choose any four and leave the final one to you. Yours is the only one that opens the lock.
Nothing is added or taken away and you can do this close-up or on stage since it is a large, solid padlock. The keys are all different and no gimmicks to dispose of. Really wonderful effect.
(Notice: Includes: Printed Instructions.)( Post Source: martinsmagic.com - click for details )