Combination locks are locks that open only when their dial is turned to a predetermined position or sequence of positions on its dial face. These positions may be numbers, letters or symbols. Typically constructed of steel, combination locks are also often coated to resist corrosion. Combination locks retain a reputation for durability and reliability and are utilized in a wide range of applications.
The archetypal combination locks are single-dial, which are usually found in padlocks and safes, as well as multiple dial, used commonly on bikes and briefcases. A single-dial lock consists of indented, parallel discs in accordance with a particular symbol and rotation sequence. Most often, the rotation acts in accordance with a clockwise-counterclockwise pattern. Once the appropriate sequence and rotational patterns are entered, each discs' indentations line up with one another and the lock can be opened. The less secure multiple-dial locks merely involve a toothed pin and several notched, rotating discs; the lock can be opened when the teeth on the pin line up with the notches on the disks. It is the simplicity of this mechanism that makes it the least reliable. More proficient manufacturers of combination locks design false gates in the discs, which, in turn, makes picking the lock extremely difficult. In fact, a lock with four discs can use up to 100,000,000 possible combinations, so with many combination locks these days, guessing the correct combination is very improbable. In addition, progress in technology has made the electronic combination lock an option. This mechanism uses a keypad, requiring the user to punch in a code for access. Just like the other, less advanced combination locks, though, these locks hold their own mechanism-specific deficiencies, one of which involves the noticeable corrosion of specific numbers on the keypad, thus exposing its access code to any tamperers.
