Wonder Treasure Box
A puzzle with a real reward!
You place an ordinary bill in this special box, and they cannot remove it without knowing the secret!
Of course, this box comes with printed instructions on how to open it, but you don't have to give them the instructions unless you want to.
Great way to give someone a gift of money- lock the money in this box first, then let them try to figure out how to get at the cash!
You can also borrow a signed bill to do this trick for any audience.
Astounding, puzzling and perplexing!