Combination Locks: Opening by Code Instead of Key

Multiple-Dial Locks

The simplest type uses several rotating discs or rings side by side, each marked with numbers or symbols. Wikipedia describes this design as common on bicycle locks, briefcases and suitcases. A notch on the inside of each disc must line up with a pin or shackle; when all the notches align, the lock opens.

Single-Dial Locks: Wheels, Gates and a Fence

Safe locks and many padlocks use a single dial. Wikipedia's account of the rotary combination lock describes the main parts:

• Wheels. Usually three or more notched wheels stacked on one axis, called the wheel pack.
• Gates. A notch in each wheel.
• Fence. A bar that can drop into the gates only when every gate is lined up.
• Drive cam. A cam attached to the dial's spindle, which picks up the wheels one at a time as the dial turns.

The user turns the dial in alternating directions to bring each wheel to its number. Once all the gates are aligned, the fence drops in and the lock can be opened. The number of wheels sets how many numbers are in the combination.

Many safe locks add protections that do not depend on the code. Wikipedia describes a relocker, or "relock trigger," as a part of the lock designed to engage the bolt if the lock is attacked, for example if the dial spindle is punched through. See safe for how relockers fit into safe design.

Push-Button and Keypad Locks

Mechanical push-button locks enter the code by pressing buttons instead of turning a dial. Locksmith Ledger traces one well-known line to the Montreal entrepreneur Aaron Fish:

• In 1961, John Marrett of Bell Canada asked Fish for a mechanical keyless access-control system.
• The Unican push-button lock launched in 1964, with Bell Canada placing the first 50 orders.
• Fish sold the company to the Kaba Group in 2001.
• The 2015 merger of Dorma and Kaba formed dormakaba.

The Ledger article, illustrated with the Simplex 1000, calls the mechanical push-button lock "ubiquitous."

Electronic keypad locks store the code in circuitry. They are covered under electronic locks.

History

Antiquity and the medieval Islamic world. Wikipedia reports that the earliest known combination lock was excavated from a Roman-period tomb in the Kerameikos in Athens, attached to a small box. Firmer evidence comes from museum collections. The David Collection in Copenhagen holds part of a brass box with a combination lock made by the astrolabe maker Muhammad ibn Hamid al-Asturlabi al-Isfahani in 1200–1201. The collection notes that al-Jazari described a similar lock around the same time. The lock has four double dials, each with 16 positions, which the museum says allows 4,294,967,296 combinations.

Nineteenth century. Wikipedia notes that U.S. patents for combination padlocks by J. B. Gray (1841) and J. E. Treat (1869) "describe themselves as improvements," suggesting such mechanisms were already in use.

Changeable bank locks. According to a Locksmith Ledger corporate profile, in 1857 James Sargent designed the Magnetic Bank Lock, which it calls "the first lock that allowed for a combination to be easily reset with a special key". The profile says the U.S. Treasury adopted it, and that in 1865 Sargent partnered with Halbert Greenleaf to form what became Sargent & Greenleaf.

The single-dial padlock. John Junkunc's U.S. Patent 948,280 was filed May 25, 1909 and granted February 1, 1910. Wikipedia calls it "the first commercially viable single-dial combination lock" and identifies Junkunc as owner of American Lock Company.

Standards for Safe Locks

UL 768 (United States). UL 768, Combination Locks, is a paid standard. UL's public summary says it covers combination locks "intended for attachment on doors of safes, chests, vaults, and the like." It tests their ability "to resist unauthorized opening … by sense of sight, touch, or hearing." The locks may or may not also resist force, and electronic locks are excluded. The current edition is the eighth, last revised August 22, 2023. Manufacturers label models by UL group. For example, dormakaba's La Gard brochure lists models as UL Group 1, Group 2 or Group 2M. The group definitions are in the paid text and are not given here.

EN 1300 (Europe). BS EN 1300:2018 classified high-security locks by their resistance to unauthorized opening. BSI lists it as withdrawn on September 29, 2023. The same La Gard brochure still labels models as EN 1300 class B or C.

Federal specifications. U.S. government containers use federal lock specifications. FF-L-2740B covers electromechanical combination locks that protect national-security information. It requires, among other things, that a lock "resist opening through manipulation for a period of 20 man-hours" and resist covert entry for 30 man-minutes. GSA's container guidance lists FF-L-2740 locks for some container classes and FF-L-2937 mechanical locks for others.

Managing Combinations

A combination is only as secure as the people who know it. U.S. rules for classified containers (32 CFR 2001.43) require combinations to be changed when the equipment is first put into use and "whenever a person knowing the combination no longer requires access to it," along with other events. Those rules apply to government containers, but the principle carries over to any shared code: change it when the group that knows it changes.

Some locks also limit when a correct code works. Those are covered under time locks.

Related Topics

• James Sargent
• Time locks
• Safes
• Padlocks
• Electronic locks
• Disc detainer locks
• UL 437
• High-security locks
• Key control
• Harry Soref: Master Lock combination lock, 1935

Sources