Dream Lock -- Mentalism Magic
A borrowed ring is locked on a 4-digit combination lock. The dials are mixed and the spectator can test the lock to show that it cannot be opened. Spectator holds the lock and is asked to think of any 4-digit number. Spectator then dials the thought-of number on the lock. This proves to be the secret code that opens the lock! No need to preset the lock or force any pre-conditioned numbers.