As soon as man had something of value, the first thief was born. And from that – the first security. But as that required actual guards, that became somewhat labor intensive, and so the lock was born. Or rather knots. Intricate knots were the first form of lock, designed primarily to act as a sign to see if a container or door had been tampered with. The deterrent aspect was secondary, as anyone with a knife could cut the thing off pretty quickly.

Then came the actual mechanical lock. It is estimated to be four thousand years old, and cultures such as the Greeks, Romans, and Egyptians developed them independently of each other roughly around the same time period. The key is inserted and the bolt is pushed the proper point. To lock the door the string was pulled to extract the cylinder, which would also pull the bolt closed. This kind of lock is still used today in certain parts of the world.

The warded lock came next, developed in Antiquity. It is believed to be first developed in China. The most basic warded lock works by a set of obstructions, generally concentric plates that poke outwards, blocking the rotation of a key that isn’t made for that lock. Only a special key that has notches cut to allow the obstructions to go through when turned works. But these keys have the same problem: By removing everything but the most essential part of the key, the part that operated the bolt, you could entirely bypass the obstructions, creating a skeleton key.

There were also developed into puzzle locks, which were varied in design, but typically obscuring the locking mechanism and required a small puzzle to be solved before the lock would open. The modern day ancestor of this lock would be the combination lock.

The modern pin tumbler lock was invented in 1848 by Linus Yale Senior. In 1861, his son (Linus Yale Junior) improved upon the design, creating a flatter smaller key with better notches. The design is too complicated to explain in detail here, but works by using a series of spring-loaded pins that when pushed in by the teeth on the proper key, will allow the plug cylinder to turn and unlock the mechanism.

The newest generation of electronic locks have been developed over the last few decades. These locks forgo using mechanical keys to unlock, instead using electronics to allow entry upon the correct sequence or keycard.