Inspired by the Sensor Envelope:
This is What Happens: In essence the performer slides a small envelope across the table and asks the spectator to confirm that the envelope is opaque and secure. The spectator will also agree that anything sealed within the envelope would remain unseen. The spectator is bound to agree once he has checked the envelope. He is next asked to select a card freely from a spread of face-down playing cards on the table.
Once selected the name of the card is written down for later verification and sealed in the envelope. The envelope is passed back to the magician who then seals it into a larger envelope and passes the two-envelope package back to the spectator for his safe keeping.
The pack of cards can now be shuffled. It is spread face up by the magician. The magician writes the name of a card on a slip of paper and it is passed face down to another spectator. The first spectator returns the sealed envelope package to the magician and it is ripped open and the inner envelope is also opened and the card bearing the name of the card in the spectator's handwriting is turned over. The magician's piece of paper is also turned over and the magician has named the card correctly.