It is often said in security that people are an organisation’s best assets but also the biggest vulnerabilities.
While high-security safes and vaults offer excellent physical protection against burglary attempts, they are highly vulnerable for one reason: people. Authorised people need to be able to unlock and access the contents of safes and vaults – whether using a key, combination or biometric method. The use of two keys (held by two different staff members) is a simply and commonly used procedure that offers a degree of protection, but if both individuals are present with their keys at the same time, then the same vulnerability exists, as people can be forced, under duress, to give threat actors access.
The time delay lock (TDL), or ‘time-lock’, is designed to address this specific risk, by preventing a safe, vault or other security container from being unlocked by anyone, except during a pre-set period. It therefore delays the opening of the safe or vault. It also reduces the risk of insider theft or exploitation – for example, an employee accessing a vault out-of-hours in order to steal from their employer.
The first TDL was invented by a man who we know very little about, called Francis Pye, and who presented his device at the 1851 Fair of the American Institute in New York City. In 1857, Amos Holbrook was the first person to try to actually commercialise the TDL, patenting his design and subsequently selling a small number of his devices to banks. However, it wasn’t until 1873 that James Sargent, an American locksmith, inventor and founder of the security lock company that later became Sargent & Greenleaf (S&G), created and patented his own TDL.[1] Whether by design or timing, Sargent’s TDLs were a big commercial success. In 1880, Sargent also invented the first ‘Time Combination Lock’ – a TDL triggered by the dialling of a connected mechanical combination lock. Sargent’s time lock inventions helped to bring the company considerable revenues, particularly with the growing number of banking and safe depository institutions in North America, at a time of increasing fear of crime.
By the early 1900s, TDLs were common requirements in bank vault doors in North America and Western Europe, and insurance companies were increasingly mandating their use to maintain coverage. Aside from S&G, a number of other security lock companies began producing mechanical TDLs destined for high-security safes and vault doors, including Diebold, Mosler and Yale in the United States.
The average mechanical TDL during this period worked by first setting the safe or vault door’s combination lock, then winding the clock movement counter-clockwise to the desired number of hours. While the clock movement was running and ticking, its shaft kept a blocking lever engaged, preventing a fence from dropping even when the lock’s tumblers were aligned. When the clock completed its pre-set run, the lever disengaged and the fence dropped, enabling the bolt to be retracted to open the door. Mechanical TDLs often had several clock movements, the main purpose of which was to provide redundancy in case the first movement failed. In older bank doors, it was common to have three or four movements for additional redundancy.
TDL technology has since been further improved upon, with electronic and electromagnetic TDLs replacing purely mechanical ones, and the use of alarms and biometric sensors to further enhance the security of the safe or vault. In some countries, such as the United Kingdom, armoured vans used to transport cash or valuables are also commonly fitted with time delay technology, to help counter armed robberies. While technology such as this helps to deter, delay or mitigate specific types of attacks, threat actors – such as criminals and hostile intelligence operatives – will always adapt and find new vulnerabilities to exploit.
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