A large bill (at least a $20) is secured in the plastic frame and a padlock is snapped shut through the frame. Six keys are shown to the spectators. It is demonstrated that only one of the keys will open the lock. The keys are mixed up in a bag. Five volunteers are given a free choice of key leaving one left for the magi. They are told that if their key opens the lock and releases the $20.00 bill it will be theirs to keep. Before each volunteer is asked to try his or her key, they are asked if they would like to trade it for the key you are holding. Each person in turn tries their key, unfortunately none of the keys work the lock. The only key left is for the magi, which happens to open the lock. The magi therefore retains the cash.
This is a great effect to use as a sucker trick at a kid's party. Children love the chance to win some money. If you use a smaller amount like a $2.00 bill it is a great way to control a win to the birthday boy or girl who acts as the magi.