Combination lock

The rotary combination locks found on padlocks, lockers, or safes may use a single dial which interacts with several parallel discs or cams.

[citation needed] In 1978 a combination lock which could be set by the user to a sequence of his own choosing was invented by Andrew Elliot Rae.

[8] At this time the electronic keypad was invented and he was unable to get any manufacturers to back his mechanical lock for lockers, luggage, or brief-cases.

The patent expired and the original mechanical invention was instantly manufactured and sold worldwide mainly for luggage, lockers, and hotel safes.

Many doors use combination locks which require the user to enter a numeric sequence on a keypad to gain entry.

Electronic combination locks, while generally safe from the attacks on their mechanical counterparts, suffer from their own set of flaws.

If the arrangement of numbers is fixed, it is easy to determine the lock sequence by viewing several successful accesses.

Similarly, the numbers in the combination (but not the actual sequence) may be determined by which keys show signs of recent use.

Exploded view of the rotating discs. The notches on the disc correspond to the numerals in the correct combination. In this case, the combination is 9-2-4.

The discs are mounted on one side of the lock, which may in turn be attached to the end of a chain or cable. The other side of the lock, or the other end of the cable, has a pin with several protruding teeth.

When the toothed pin is inserted and the discs are rotated to an incorrect combination, the inner faces of the discs block the pin from being extracted.