If you lived in the age of Alexander the Great, your lock might have been a rope with a fancy knot to keep intruders out. Years later, the rope was discarded in favor of a heavy, wooden bar. The bar would block your door in the event that a group of ramrod-carrying men in loincloths tried to force their way into your castle. More intricate mechanical devices like padlocks and pin tumbler locks were later developed. The pin tumbler lock introduced a key into the equation, which quickly became a status symbol. If you owned a key, this broadcast to the masses that you had property to protect. Now, virtually everyone has a key lock of some sort on their home.