Lock Bumping: What Property Owners Need To Know

Posted on: 11 December 2014

Lock bumping is a method that some criminals use to pick pin tumbler locks. It's relatively easy to learn how to open a lock this way, and an increase in 'how-to' videos online has led to a surge in lock bumping incidents across the United States. If you want to protect your home against this security threat, learn how lock bumping works and find out how you can make it harder for thieves to get access to your property in this way.

How tumbler pin locks work

The principle behind a standard pin tumbler lock has remained largely the same for more than a century. Each lock features two sets of pins. A locksmith cuts the lower pins at different heights to match the shape of a key, and a set of springs push down the upper (driver) pins so they touch the tips of the lower pins.

When you insert the right key, you lift the lower pins to push up the driver pins in a certain way, creating an even shear line. This allows the lower and driver pins to separate, and you can then turn the key. The inner piece of the lock (the plug) then rotates and activates the locking bolt to let you open the door.

You can find this design in millions of locks, including deadbolts, padlocks, mailboxes and even some cars. Unfortunately, the design has a simple, but crucial flaw.

The flaw in tumbler pin locks

The tumbler pin lock design seems secure because you cannot turn the lock unless the lower and drive pins completely align. You cannot get this alignment unless you have the exact key. Unfortunately, a bump key can work around this problem.

The bump key uses force to violently jump the pins. You simply use a special key to strike the pins, causing the lower and driver pins to briefly separate. In the short time that the pins separate, you can use the bump key to turn the lock and gain entry to the property.

Getting a bump key

You can't just use any key to bump a lock. You need to buy a key that is the right size for the lock, but you must cut each ridge on the key as deep as possible. Some locksmiths refer to bump keys as '999 keys' because they cut the keys to a depth of nine in a conventional key-making machine. It's also relatively easy to buy bump keys online.

Several state and federal laws prevent locksmiths passing on specialist equipment (including bump keys) to anyone outside the industry. A specific postal statute also prohibits the sale or traffic of any key that you can use to open a post office lock. That aside, these laws do not prevent criminals and unscrupulous dealers passing on the materials you need to bump a lock. If you have the right type of key, you can often create a bump key by filing down the key yourself.

Why lock bumping is a serious issue

According to the Federal Bureau of Investigation (FBI), there were more than 2.2 million burglaries in the United States in 2010, which accounts for 23.8 percent of all property crimes. The FBI also reports that around 33 percent of these burglaries occurred without force. In many cases, these burglaries involved lock bumping, but it's difficult to confirm when this happens because you can't tell when somebody has bumped your lock.

To make matters worse, your insurer will not always pay a claim for burglary when there is no sign of forcible entry. Ironically, new locks are often more vulnerable because modern key-making processes are more precise. These enhanced mechanics actually make it easy to carry out the bumping process.


Several manufacturers now produce high-security bump-resistant locks. These devices feature extra pins, bars and other components that stop the lock bumping process working. In many cases, these locks include features where you can replace a key without changing the lock.

Of course, most thieves act on an opportunistic basis, so you should also take other steps to improve home security. Motion-activated lights, door chains and alarm systems may all deter a potential burglar, even if you still have a conventional tumbler pin lock.

Lock bumping is an increasing problem in the United States and can leave your home vulnerable even when you lock the doors. To make sure a thief cannot bump your locks, talk to a specialist locksmith for more advice.