When it comes to changing combinations on safes and vaults, locksmiths rely on a variety of tools. The first step is to use a small probe or screwdriver to turn the dial to the left at least four revolutions and stop at 0. Then, quickly turn the dial to the right one revolution. As you approach 0, you should feel and hear the drive cam pick up the wheel adjacent to the drive cam (the third wheel in a three-wheel package).
Continue spinning rapidly through a second revolution. When you get closer to 0 again, you should feel and hear the third wheel when it picks up another wheel (the second wheel in a three-wheel package). One more revolution and the same sound and feel will be felt when you pick up the first wheel. Any additional rotation of the dial should show no difference in sound or feel.
By doing this, you can determine that there are three wheels (and combined numbers) on your lock. Another method used by locksmiths is called “determining the extent of the key exchange hole”. This involves drilling a hole that will allow them to place their sight in a position to observe the change in the key hole. By turning the dial and looking for certain reference points on the combination lock wheel package through the shift key hole, it is possible to obtain the combination and then open the safe normally.
This method is preferred by professional safe specialists as it leaves the lock in good working order and only simple repairs are needed to return the safety barrier to its original state. Criminals rarely use this technique due to its expensive tools and in-depth knowledge required of locking systems.