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Area Safe & Lock Service
3301 Mount Vernon Ave
AlexandriaVA 22305
 (703) 684-6161

What Is Lock Bumping and How Can I Prevent It?

What Is Lock Bumping and How Can I Prevent It?

As you read this article, somewhere a burglar is reading up on how to enter your home by bumping the lock. Most pin and tumbler locks (the vast majority used for residential security) can be defeated by simple tools and what is known as "bumping." 

Originally developed by honest, professional locksmiths to make their jobs easier, knowledge of this technique has spread rapidly and now constitutes a known threat from thieves. So what is lock bumping and how can you protect yourself from the growing number of criminals learning this technique? Keep reading to find out. 

How Do Pins and Tumblers Work?

Inside the common lock is a set of small cylinder-shaped pins in channels kept under downward pressure by springs. Each channel has a set of two pins, one on top of the other. The top pin is the "driver," the lower pin is simply known as the "pin." The pins below have different lengths while the drivers above are uniform in length. The drivers are pressed downward by the springs and touch the pins when the lock is engaged. 

The cylinder encasing the channels, pins, drivers and springs has what is called a "shear line." When the tops of the pins and bottoms of the tumblers come into horizontal line with the shear line, the lock can be turned or disengaged. The teeth of the key slide under the pins and raise them, according to the key's peaks and valleys until the pins and drivers all line up with the shear line. Both common deadbolt locks and in-knob locks use this system.

What Are Bump Keys?

Each lock manufacturer uses a different style of keyway, the slot into which you slide the key. Below the teeth on the shaft of your key is a system of horizontal grooves. These grooves only fit keyways designed for it.  A bump key has the right grooves only for the particular brand of lock to be bumped. So a burglar may have dozens of bump keys to gain access to any brand of lock he encounters.

A bump key has the right grooves only for a particular brand of lock, but it can access any lock in that line. A burglar may have dozens of bump keys to gain access to any brand of lock he encounters.

On the bump key, the teeth have been ground so that the valleys dip to the lowest level and the peaks are short and evenly spaced. It is slipped into the keyway, just short of full insertion, so that all the pins are resting in the valleys. Now, the burglar turns the key until it stops and, maintaining the pressure of the turn, pounds the vertical edge of the key head with something blunt, performing the so-called "bump." As the key swiftly moves forward, the peaks push the pins and drivers up with sufficient force to overcome the downward pressure of the springs. 

The torque on the key enables it to turn the lock at the moment the pins and drivers are aligned with the shear line. It may take several attempts, but the correct alignment usually occurs in just a few bumps. That means with these bump keys, thieves can have access to your home within minutes. 

Can You Prevent Lock Bumping?

Want our advice? Here it is: get better locks. A good, light commercial grade lock will have anti-bumping features and will be relatively inexpensive. A professional locksmith can install one for you or retrofit your present locks without replacing the entire assembly. Of, if you're ready to upgrade your entire home security, you could choose keyless entries, which leave no keyway for burglars to access. To see a full line of options, please view our solutions page. Also, feel free to contact Area Safe and Lock Service. Our experienced staff would be happy to answer all of your questions.