Ever since people first began having private possessions, locks to keep that property out of the hands of thieves have been designed. It has been an evolutionary process: As each lock eventually yielded to thieves' attempts to pick, or open, it, ingenious locksmiths came up with new lock and key designs.

The earliest known lock is the wooden Egyptian pin-tumbler type. It was opened by a pegged wooden key, often more than a foot long, so large that it had to be carried over the shoulder. When the key was inserted into the lock, its pegs lifted pins that held the bolt in place. The ancient Chinese used a leaf-spring padlock; the key depressed the spring, allowing the bolt to slide back. The Greeks used primitive locks with large, sickle-shaped keys.

The Romans introduced metal for locks and keys and also invented the warded...