The double acting tumbler lock, also known as a level tumbler, was invented by Robert Barron in 1778. It uses a system of levers to stop the bolt from moving inside the lock. When the key is inserted, it lifts the tumblers, allowing the bolt to slide past.

While the original version of the double acting tumbler lock had two levers, these types of locks usually use an odd number of levers to maintain symmetry in the locking mechanism.

History of Tumbler Locks and Robert Barron

Tumbler locks have been around for thousands of years and have been improved over time. However, the basic system fundamentals are the same. The earliest locks of this type involved a wooden peg that fell into a hole, lifting out of the way to unlock using a device that looked like a wooden toothbrush.

This is the fundamental system that all tumbler locks use, and remained unchanged for many years, only improving in lock and key intricacy, making it hard to pick the lock.

In 1778, Robert Barron patented the double acting tumbler lock. This patent laid the groundwork for the mechanism that we still use today. Barron's lock had two levers that had to be lifted out of the way at a precise height to unlock the lock. This was a drastic change to what lockpickers had previously encountered, revolutionizing the lock industry.

How Double Acting Tumbler Locks Work

A double acting tumbler lock is made out of levers that must be moved out of the way by a corresponding key for the bolt to move. The levers have pockets which the bolt moves through while unlocking. While the original tumbler had two levers, most today have three or five levers, improving the security level.

Three-lever locks are commonly used for low-security situations, such as inside doors. Key tolerance is lower, as there is a smaller amount of combinations for keys, and some keys may be able to open locks that they shouldn't.

Five-lever locks provide enhanced security and are typically recommended and can be a prerequisite for acquiring home insurance policies. The five levers provide greater key combinations and higher key tolerance. More advanced locks may have additional notches cut into the bolt that catch the bolt, further preventing it from getting picked. This is similar to how a pin tumbler system works.

Advantages and Disadvantages

A double acting tumbler lock is known for its high level of security; however, it can still be picked. A curtain pick is used to pick these locks. A tool is inserted into the key entry, and force is applied to the locking bolt. The pick then lifts each of the levers to the correct height, allowing the bolt to pass and unlock.

Bump keys can also be used on these kinds of locks, especially the three-lever ones. Five-lever locks provide a higher degree of security, as key combinations are more plentiful, lowering the likelihood of a bump key working.

These locks can also be drilled, but usually require a trained locksmith to perform this correctly and successfully. Since these locks are usually hidden from sight, a novice lockpicker may be unable to find the drilling point easily.

The Takeaway

While we have come a long way in the development of locks and security mechanisms, the central concept of how they work has remained the same. Robert Barron's double acting tumbler lock system of levers is used to hold a locking bolt in place. Once these levers are lifted to the correct position, the lock opens. Essentially, even the most advanced tumbler locks follow this system.

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