Humans have long used locks and keys to protect their valuables and properties. Researchers are uncertain when and where the first systems of locks and keys were used, but evidence points to the use of locks more than four thousand years ago. Early examples of locks and keys being used were found in Ancient Greece, Persia (Iran) and Asia (primarily China). These societies developed their own locking designs and technologies without influence from one another.
Early pin tumbler locks were made of wood and were used to protect dwellings. These locks were effective for a time, but they also had many drawbacks – they could only be opened from one side of the door and they could also be easily broken or damaged.As metal working abilities improved in the final two centuries leading to the common era, more technical and effective locks were produced. Roman Empire locks during this time were frequently made form iron and more secure from contemporary products from Greece and Egypt. Iron lock keys were made small enough to be carried in pockets or worn on rings. Advancements in lock technology came to a halt, however, with the end of the Roman Empire in the first century of the common era.
Steel lock, 18th century. (Photo: SSPL) 
A forged iron lock for a front door. Netherlands, 1700 – 1800. (Photo: Sepia Times) 
Lock, 16th century, German, Iron. (Photo: Sepia Times) 
The key is guided into the lock by a bar fitting into a groove at the end of the wards, which strike against two pins to move the bolt. 
Lock and key made by E Cotterills of Birmingham complying with the ‘Acme’ patent of Peter Wilson, which covers a key acting through holes in the levers. 
Bramah padlock and key, 1801. (Photo: SSPL) 
Henry Maudslay (1771-1831), one of Britain’s greatest engineers, made this padlock while he was working as a craftsman for Joseph Bramah in London. The lock was placed in the window of Bramah and Co’s shop with a board offering a reward. The lock stayed in the window un-picked for 50 years until 1851 when it was opened by A C Hobbs, an American locksmith, who came to London for the Great Exhibition and took on the challenge. He took 16 days to open the lock and receive his reward. Chubb now own Hobbs’ world famous firm. (Photo: SSPL) 
Joseph Bramah, English inventor, late 18th century. (Photo: SSPL)
Incredibly, little advancement would be made in lock technology until more than 1600 years later! The 18th and 19th centuries saw many technological advancements, many of which influence present-day locks and keys. British engineer Joseph Bramah developed the first high-security designed locks in the late 18th century (and the Bramah company remains in business nearly two and a half centuries later!). Robert Barronin, Jeremiah Chubb, Linus Yale and James Sargent were other engineers whose designs advanced locking technologies during this time.
Pen portrait of Linus Yale (1821-1868), the American locksmith who invented the Yale pin-tumbler cylinder lock which enabled smaller keys to be used than in the past. (Photo: SSPL) 
The yale lock was invented by Linus Yale Jr between 1860 and 1868. His cylinder lock used pin-tumblers similar to those used in ancient Egyptian locks. The flat key is inserted and its serrated upper edge raises each pin to the correct height so that the inner cylinder can be turned. (Photo: SSPL) 
Yale lock, 1860-1970. (Photo: SSPL) 
Large model of a Yale lock with key, 1970. (Photo: SSPL)
Samuel Segal and Harry Soref were early 20th century engineers whose inventions brought more security to locking systems. Their designs, as well as those of the aforementioned engineers, influence the majority of today’s locking and key designs. The 1917 invention of the Mechanical Key Duplication Machine, in the United States, allowed for the proliferation of the flat metal keys we are familiar with today.
UIG’s historical archive features many examples of ancient keys and locks, as well as portraits of the important inventors and engineers.
Sources:
http://www.historyofkeys.com/locks-history/history-of-locks
https://www.historicallocks.com/en/site/h/articles/historyaboutlocks/history-of-keys
https://www.brown.edu/Departments/Joukowsky_Institute/courses/13things/7639.html