A Chubb detector lock is a type of lever tumbler lock

Lever tumbler lock

A lever tumbler lock is a type of lock that uses a set of levers to prevent the bolt from moving in the lock. In the simplest of these, lifting the tumbler above a certain height will allow the bolt to slide past. The number of levers may vary, but is usually an odd number for a lock that can be...

 with an integral security feature which frustrates unauthorised access attempts and indicates to the lock's owner that it has been interfered with. When someone tries to pick the lock or to open it using the wrong key, the lock is designed to jam in a locked state until (depending on the lock) either a special regulator key or the original key is inserted. A person attempting to pick a detector lock after triggering the automatic jamming mechanism has the additional problem of resetting the detector mechanism. This introduces additional complexity into the task, thereby increasing the degree of lock-picking skill required to a level which very few people would have. The first detector lock was produced in 1818 by Jeremiah Chubb of Portsmouth

Portsmouth

Portsmouth is the second largest city in the ceremonial county of Hampshire on the south coast of England. Portsmouth is notable for being the United Kingdom's only island city; it is located mainly on Portsea Island...

, England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

, as the result of a Government competition to create an unpickable lock. It remained unpicked until the Great Exhibition

The Great Exhibition

The Great Exhibition of the Works of Industry of all Nations or The Great Exhibition, sometimes referred to as the Crystal Palace Exhibition in reference to the temporary structure in which it was held, was an international exhibition that took place in Hyde Park, London, from 1 May to 15 October...

 of 1851.

Development

Jeremiah Chubb, who was working with his brother, Charles, as a ship's outfitter and ironmonger in Portsmouth

Portsmouth

Portsmouth is the second largest city in the ceremonial county of Hampshire on the south coast of England. Portsmouth is notable for being the United Kingdom's only island city; it is located mainly on Portsea Island...

, invented and patented his detector lock in 1818. In 1817, a burglary in Portsmouth Dockyard

HMNB Portsmouth

Her Majesty's Naval Base Portsmouth is one of three operating bases in the United Kingdom for the British Royal Navy...

 which had been carried out using false keys to gain entry prompted the British Government to announce a competition to produce a lock that could be opened only with its own key. Building on earlier work by Robert Barron

Robert Barron (locksmith)

Robert Barron was an English locksmith notable for his invention of the double–acting tumbler lock in 1778.-References:...

 and Joseph Bramah

Joseph Bramah

Joseph Bramah , born Stainborough Lane Farm, Wentworth, Yorkshire, England, was an inventor and locksmith. He is best known for having invented the hydraulic press...

, Jeremiah developed a four-lever lock that when picked or opened with the wrong key would stop working until a special key was used to reset it. This security feature was known as a regulator, and was tripped when an individual lever was pushed past the position required to bring the lever in line to open the lock. As a result of this innovation, Jeremiah was able to claim the £100 reward offered by the Government.
A convict aboard one of the prison hulk

Hulk (ship)

A hulk is a ship that is afloat, but incapable of going to sea. Although sometimes used to describe a ship that has been launched but not completed, the term most often refers to an old ship that has had its rigging or internal equipment removed, retaining only its flotational qualities...

s in Portsmouth Docks was given the Chubb lock with a promise of a free pardon from the Government and £100 from Jeremiah if he could pick

Lock picking

Lock picking is the art of unlocking a lock by analyzing and manipulating the components of the lock device, without the original key. Although lock picking can be associated with criminal intent, it is an essential skill for a locksmith...

 the lock. The convict, who was a locksmith by trade and had successfully picked every lock he had been presented with, was confident he could do the same with the detector lock. After two or three months of trying he was forced to admit defeat.

Manufacture and improvements

In 1820, Jeremiah joined his brother Charles in starting their own lock company, Chubb

Chubb Locks

Chubb Locks is a brand name of the Mul-T-Lock subsidiary of the Assa Abloy Group, which manufactures high security locking systems for residential, secure confinement and commercial applications.-History:...

. They moved from Portsmouth to Wolverhampton

Wolverhampton

Wolverhampton is a city and metropolitan borough in the West Midlands, England. For Eurostat purposes Walsall and Wolverhampton is a NUTS 3 region and is one of five boroughs or unitary districts that comprise the "West Midlands" NUTS 2 region...

, which was the lockmaking capital of Great Britain, and opened a factory in Temple Street. In 1836 they moved to St James' Square in the same town. A further move to the site of the old Workhouse

Workhouse

In England and Wales a workhouse, colloquially known as a spike, was a place where those unable to support themselves were offered accommodation and employment...

 in Railway Street followed in 1838. The Chubb lock reportedly became popular as a result of the interest generated when George IV

George IV of the United Kingdom

George IV was the King of the United Kingdom of Great Britain and Ireland and also of Hanover from the death of his father, George III, on 29 January 1820 until his own death ten years later...

 accidentally sat on a Chubb lock that still had the key inserted. A number of improvements were made to the original design over the years but the basic principle behind its construction remained unchanged. In 1824, Charles patented an improved design that no longer required a special regulator key to reset the lock. The original lock used four levers, but by 1847 work by Jeremiah, Charles, his son John and others resulted in a six-lever version. A later innovation was the "curtain", a disc that allowed the key to pass but narrowed the field of view, hiding the levers from anybody attempting to pick the lock. Eventually, Chubb began to manufacture brass padlocks incorporating the "detector" mechanism.

Picking

Competition in the lock business was fierce and there were various challenges issued in an attempt to prove the superiority of one type of lock over another. Joseph Bramah exhibited one of his locks in the window of his shop and offered 200 guinea

Guinea (British coin)

The guinea is a coin that was minted in the Kingdom of England and later in the Kingdom of Great Britain and the United Kingdom between 1663 and 1813...

s (£210) to anybody who could devise a method of picking it. In 1832, a Mr Hart, replying to a challenge by Chubb, failed to pick one of his detector locks. After a number of people tried and failed, the first person to pick the six-lever Chubb lock was Alfred Charles Hobbs

Alfred Charles Hobbs

Alfred Charles Hobbs was an American locksmith.He was born in Boston, Massachusetts in 1812 and married Charlotte F. and had a child: Alfred J. Hobbs...

, the inventor of the protector lock

Protector lock

The Protector lock was an early 1850s lock design by renowned American locksmith Alfred Charles Hobbs, the first man to be able to pick the six-levered Chubb detector lock at the Crystal Palace Exhibition in the year 1851, which was created with the intent of being a lock that could not be...

, during the Great Exhibition in 1851.