Safecracker

Safe-cracking is the process of opening a safe without either the combination or key.

Different procedures may be used to crack a safe, depending on its construction. Different procedures are required to open different safes so safe-crackers need to be aware of the differences.

The most surreptitious way of cracking a safe is to the lock in order to obtain the combination required to open the safe without actually damaging the safe.

Some rotary combination locks can be manipulated by feel or sound in order to determine the combination required to open the safe. More sophisticated locks use wheels made from lightweight materials which reduces this vulnerability. Another anti-manipulation mechanism is serrated wheels (false tumbler notches) that make tactile techniques much more difficult. Another defence is a clutch-type driver wheel that prevents contact of the fence to the tumblers except in one position. These locks can be identified by a "click-click" feeling in the dial or by a dial that is pushed in and turned. Manipulation is the locksmith's preferred choice in lost-combination lockouts, since it requires no repairs or damage, but can be extremely time consuming due to lock improvements over the years, and is also a difficult art to master. There are also a number of tools on the market to assist safe engineers in manipulating a combination lock open. These generally fit directly on to the locks dial and assist in being able to accurately read the left and right contact points of the locks drive cam.

Some combination padlocks can also be manipulated by pulling and applying leverage on the shackle while turning each dial to determine the combination required to unlock them.

In the absence of any other information regarding the safe's combination, a combination lock may be opened by dialing every possible combination. Many combination locks allow some "slop" in the settings of the dial, so that for a given safe it may be necessary only to try a subset of the combinations. Such "slops" may allow for a margin of error of plus or minus two digits, which means that trying multiples of five would be sufficient in this case. This drastically reduces the time required to exhaust the number of meaningful combinations. A further reduction in solving time is obtained by trying all possible settings for the last wheel for a given setting of the first wheels before nudging the next-to-last wheel to its next meaningful setting, instead of zeroing the lock each time with a number of turns in one direction.

Safes may be compromised surprisingly often by simply guessing the combination. This results from the fact that manufactured safes often come with a manufacturer-set combination. These combinations (known as try-out combinations) are designed to allow owners initial access to the safes so that they may set their own new combinations. Sources exist which list manufacturers' try-out combinations.

...
Wikipedia