The History of Locksmithing
The most primitive forms of fastening were by means of knotted thongs, or a wooden or metal bar placed across the inside of a door. A curved key, shaped somewhat like a sickle, was used to move the bar, and examples have been found in many parts of northern Europe. The earliest locks of all are probably the Chinese, of which some extant specimens are as secure as any made in Europe up to the 18th century. Some Egyptian locks are known to be 4000 years old, and locks on the Egyptian plan may be found in many remote places in Europe. The Egyptians made the portion of the hole into which the retaining pegs were inserted hollow, and the key had pins upon it corresponding with these pegs. The key was inserted into the end of the bolt. The Romans based their locks on the same principle as the Egyptians, but the bolt was smaller and the dropping pins were pressed downwards by a spring.
Mechanical locks were developed by the Egyptians about 2000 B.C. Their locks were made of wood and contained pegs that fell by gravity into corresponding holes in the lock bolt. A wood key with a similar pattern of pegs was used to raise the pegs and slide back the bolt. The Greeks used a simple lock in which a notched bolt was moved by a large sickle-shaped key. The Romans developed warded locks and small keys.
The early English and medieval keys were the forerunners of the modern keys from a mechanical point of view. In the locks of this period a pivoted tumbler was used instead of dropping pins. A number of impediments contained in the lock case were interposed between the key and the bolt; these are called wards, and the portion of the key which enters the lock is formed so as to escape them. Robert Barren improved the mechanism of locks in 1774 by placing two levers to guard the bolt, instead of only one; and he also made it necessary for the levers to be lifted up to the right height before the bolt could be turned. The Bramah lock was invented . by Joseph Bramah (1749-1814) in 1784. It has a number (generally six) of thin metal plates called sliders, the notches of which must be brought into certain positions before the key can be used. The Chubb lock was patented in 1818, and since then has been altered and improved many times. It is a lever lock, and has more levers than usual with the addition of one called the detector. This is so placed that it moves and fixes the bolt if any of the levers be lifted a little too high. Notice is thus given of any attempt at picking the lock, even if unsuccessful, as the rightful key will not then open the lock until it has first been turned the reverse way. Both the Bramah and Chubb locks were erroneously thought to be 'unpickable'.
In medieval Europe, warded locks became very elaborate and keys again became large and cumbersome. The lever-tumbler lock was invented and came into general use in the 18th century. It has been largely replaced by the pin-tumbler cylinder lock, invented in 1865 by an American, Linus Yale, Jr. (1821-1868).
The Yale lock was an American invention of about 1860. It is a tumbler lock, but the small flat key and the keyway interlock throughout their length owing to their peculiar cross-section. It is a modern adaptation of the old Egyptian lock, which had pins made of wood, whereas the modern pin-cylinder lock has metal pins.