We supply you what appears to be a regular Resetable Combination Padlock which is normally opened by setting the four digits on the lock.
However the lock supplied has been cleverly gimmicked, so that it can be made to open using the four digits apparently selected at random by a spectator. It can be used for several mental effects, and we have detailed some presentation ideas in the instructions that accompany the item.
You first demonstrate the lock cannot be opened by any random series of numbers. Have a couple of spectators try with different random four digits numbers. You can ask spectators to call out four digits, and have a spectator set these on the lock, to demonstrate it will not open. Then hand it over to a spectator who confirms you have never met before, and have him use his year of birth as the secret combination, and the lock will open.
Or if there is a young married lady or gent (look for the Wedding band on the finger), you could have them use their year of marriage. Lock their wedding ring (or rings) on the lock, then spin the numbers and ask them to try and open the lock with random numbers. Then you demonstrate that their year of marriage is the magic number that opens the lock.
We have gimmicked these high quality brass locks which are not always available in the market. Our stock of these is limited so please order early if interested.