Simplex or Unican 5-button all-mechanical combination locks are usually used in a variety of secure but high-traffic applications, and come in a number of flavors: dead bolt, slam latch, lock switches for alarms, buttons in a circle or a vertical line, etc. The internal locking works are the same across all of these
Contrary to what the marketing reps would have you believe, the locks can be opened fairly quickly without knowing the set combination and without damaging the lock. Through a blend of a soft touch, a little hard logic, and an implicit understanding of how the locking mechanism works, they generally yield within five minutes or so.
How to Defeat Simplex 5-Button Combination Locks features the mechanical workings and a method of defeating the lock that falls out by logical inference and observations from playing with it.