Lock and key

A lock is a mechanical device for securing a door, chest, or other receptacle so that it can only be opened by an authorized person. Most locks are opened by a key which is placed in the lock and turned. Combination locks do not use a key but rather have a cylinder that is turned to certain stops. Today, many hotels use special plastic cards with magnetic strips as keys which cause a door to open electronically when inserted in a slot near the doorknob.

History

The lock originated in the Near East, and the earliest known lock to be operated by a key was the Egyptian lock. Possibly 4,000 years old, this large wooden lock was found in the ruins of the palace of Khorsabad near Nineveh, the ancient capital of Assyria. The Egyptian lock is also known as the pin-tumbler type, and it evolved as a practical solution to the problem of how to open a barred door from the outside. The first and simplest locks were probably just a bar of wood or a bolt across a door. To open it from the outside, a hand-size opening was made in the door. This evolved into a much smaller hole into which a long wooden or metal prodder was inserted to lift up the bar or bolt. The Egyptians improved this device by putting wooden pegs in the lock that fell into holes in a bolt, which meant that the bolt could not be moved until the pegs were lifted out. This was done by giving the long wooden key some corresponding pins that lifted out the pegs from the holes in the bolt so it could be drawn back. These locks were up to 2 ft (61 cm) long and their keys were long, wooden bars resembling a toothpick. It was this invention of tum blers—small, movable wooden pegs that fell by their own weight into the bolt—that would eventually form the basis of modern types of locks.

The ancient Romans built the first metal locks, and their iron locks and bronze keys are easily recognizable even today. They improved the Egyptian model by adding wards—projections or obstructions inside the lock—that the key must bypass in order to work. Besides these warded locks, the Romans also invented the portable padlock with a U-shaped bolt which is known to have been invented independently by the Chinese. Some Roman locks used springs to hold the tumblers in place, and the Romans made locks small enough that they could wear tiny keys on their fingers like rings. In medieval times, locks and keys changed little in design, with most of the effort directed at making them more elaborate and beautiful. It was during this time that lock-making became a skilled trade, and although there were some design changes, like a pivoted tumbler and more complicated wards, medieval locks are characterized mainly by their high degree of lavish embellishment. Despite this high level of medieval craftsmanship, these medieval locks did not provide a great deal of security against the determined and skilled thief, and even with especially elaborate warding systems, they were still relatively easy to pick or open.

Modern locks

The modern age of the lock and key is usually said to have begun in 1778 in England when Robert Barron first patented his double-acting tumbler lock. Also called the multiple tumbler, this ingenious design was a major advance in lock security and established the principle of all lever locks. Barron's new lock had two tumblers, which are really levers, that had to be raised to exactly the right height for the lock to open. Unless a properly notched key was used to raise each tumbler, the lock would not open. His lock could still be picked by a determined individual however, and in 1818 Jeremiah Chubb was able to improve Barron's lock by adding a "convictdefying detector." This was a spring or a special lever that was activated if any tumbler was raised too high. The lock would then jam, both preventing the bolt from releasing and showing the owner that the lock had been tampered with. Real lock security was not achieved however until English engineer Joseph Bramah (1748-1814) first introduced his pick-proof lock in 1784, after Barron's lock but before Chubb. Bramah's lock was exhibited in his shop window with a sign offering a substantial sum to anyone who could pick it. The offer outlived Bramah whose lock remained unopened for over 50 years until a skilled American mechanic finally picked it open after 51 hours of effort. Bramah's 4 in (10 cm), hand made, iron padlock was impervious because of its extreme complexity, and he soon found that he could not produce enough locks to meet the growing demand by using traditional methods. His locks used a notched diaphragm plate and a number of spring-loaded radial slides that were pushed down by a notched key until they matched the notches on the diaphragm. Producing such precision instruments on a large scale necessitated precision machine tools , and with the help of English engineer Henry Maudslay (1771-1831), Bramah produced a series of machines that were among the first machine tools designed for mass production . Thus the simple lock and key were at the forefront of a revolution in manufacturing, heralding the standardization and inter-changeability of parts and division of labor that would characterize modern methods of mass production.

By the mid-nineteenth century, the lock industry was in full force and was attempting to meet the growing demands of an economy spurred by the Industrial Revolution . In 1861, the American inventor Linus Yale Jr. (1821-1868) produced the Yale cylinder lock which was based on the pin-tumbler mechanism of the ancient Egyptians. This type of lock is still the most common type used today, and it uses a small, flat key whose serrated edges raise five pins in the cylinder to proper heights and make it possible to turn the cylinder. Varying the lengths of these five pins combined with other slight internal changes, allowed for millions of possible combinations, meaning that practically no two notched keys are alike. In an odd twist on conventional wisdom, it could be said that Yale took advantage of mass production methods to manufacture unidentical articles, since he made each set of lock and key slightly different from the one before it. While still not infallible, Yale cylinder locks are quite difficult to pick and offer reasonable security under ordinary circumstances. This style of lock and key is the most familiar and the most generally used to secure the outside doors of buildings and automobiles.

Keyless combination locks have been known since the sixteenth century. They contain a series of rings or tumblers threaded on a spindle which must be turned from the outside in such a way that all the rings line up. These rings usually have numbers or letters on them, and if a lock has three rings with 100 numbers on each, there are approximately one million possible combinations, only one of which will open the lock. Combination locks have no keyholes in which to pry or insert explosives , and they became popular for safes and vaults. They are often used in conjunction with time-lock devices, preventing a safe or door from being opened during certain hours even if the correct combination is used.

Altogether, today's mechanical locks are variations of the three basic types of locks: the early Bramah lever, the Yale cylinder, and the combination lock. Sometimes a single lock may combine some features of each, such as a Finnish combination lock whose rings must be moved to the proper position by a the turn of a key. In the United States in the 1970s, electronic locks that worked on the same principle as the touch-tone phone became popular. When the correct sequence of spring-loaded buttons was pushed, the door would open. This system used no keys, proved to be as tamper-proof as any traditional combination lock, and allowed the touch-tone sequence to be changed at any time. Magnetism has also been used to operate a Yale-type lock. These locks had keys with no serrations but rather contained several small magnets. Insertion of the key allowed its magnets to repel magnetized spring-loaded pins inside the lock which were raised to open it. The newest lock and key systems do not use anything recognizable as a traditional lock or key. Increasingly, today's hotels are switching to special plastic cards with magnetic strips on them. Like a key, they are inserted, but only momentarily, into a slot usually just above the doorknob. Often a small green light flickers after withdrawal, and the door opens if the doorknob is turned. These cards open the door using electronic systems.

Locks and keys may change considerably over time, but the universal human need to keep other people away from one's possessions will remain as important to future generations as it did to the ancient Egyptians.

Resources

books

Eras, Vincent J. M. Locks and Keys Throughout the Ages. Schiedam: Interbook International, 1975.

Hennessy, Thomas F. Early Locks and Lockmakers of America. Des Plaines, IL: Nickerson & Collins Pub. Co., 1976.

Hobbs, A. C. The Construction of Locks. West Orange, NJ: A. Saifer, 1982.

Roper, C. A. The Complete Book of Locks & Locksmithing. Blue Ridge Summit, PA: G/L Tab Books, 1990.

Leonard C. Bruno

KEY TERMS

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Combination lock

—One which is operated by a rotating dial by which certain numbers or letters in a particular order, after a given number of turns in the prescribed direction, are brought opposite the setting mark, after which the lock can be opened.

Cylinder

—The part of a cylinder lock that provides the security. It consists of a short cylindrical plug containing the key hole and mechanism, adjustable by the key.

Spindle

—The shaft of a knob or handle, usually square, which passes through the follower to enable the handle, when turned, to operate the spring bolt.

Tumbler

—A part to retain the bolt or provide security in certain locks. In England, this part is called a "lever."

Ward

—A fixed projection in a lock to prevent a key from entering or turning, unless it is properly shaped.