The Bump Key

bump key

Pin and tumbler lock diagram from Wikipedia

Bump keys pose a huge threat to home security for three reasons:

1. Bump keys can open 95% of the residential deadbolts in use in this country today.

2. Bump keys are cheap and easy to acquire by shopping on the Internet.

3. Not many people know about bump keys, so nobody’s doing anything to prevent their use.

To understand how a bump key works, we first need to learn a bit about how a deadbolt lock works.

The first concept we need to understand is the keyway. Have you ever slid a key into a lock only to discover it’s the wrong key? It still fit, but wouldn’t open the lock. Yet other keys won’t even go into the lock in the first place.

Keys with the same keyway can go into the same locks, even if they’re not the right key. And it turns out that just three keyways account for the vast majority of deadbolt locks in the United States.

The Kwikset KW1 keyway, the Schlage SC1 keyway, and the Schlage SC4 keyway account for almost every deadbolt lock in America. Take a key from one Kwikset lock and it will fit into almost any other Kwikset lock. Same for the Schlage keyways.
Furthermore, many other lock manufacturers use these same keyways. You don’t have to have a Kwikset lock to have a Kwikset KW1 keyway. There are many other locks out there that use the Schlage keyways, too.

The second concept to understand here is the combination of the lock. Most residential deadbolts have 5-pin cylinders. That means there are five pins that have to move to the correct position for the lock to open. There are typically either nine or ten possible positions for each pin.

(Most Kwikset locks are 5-pin, and use only 7 depths. That means there 7^5 possible combinations, or 16,000. There are actually somewhat fewer than this, as certain combinations aren’t allowed. Schlage locks use 10 depths. So a 5-pin Schlage deadbolt has 10^5 possible combinations, or 100,000. A 6-pin Schlage lock has a million possible combinations.)

Each pin position in the lock corresponds to a groove or cut in the key. The depth of the groove in the key determines how far it moves the pin in the lock. A groove can have a depth anywhere from 0 to 9.

A bump key is a key that is cut for a specific keyway, that has every position cut to a depth of 9. (Thus bump keys are sometimes called 999 keys.) This allows for the maximum possible movement of each pin. If every groove on they key were cut only to a depth of 8, then the bump key wouldn’t work if any of the pins were set for a depth of 9. Cutting every groove to the maximum depth of 9 allows the bump key to work on every possible pin position, from 0 to 9.

When the bump key is inserted into the lock, and banged  with a hammer or mallet, the force causes the bottom pins in the lock to bump the top pins. As the top pins pass the shear line, the lock is able to be turned and opened.

The bump key threat is scary because bump keys require no skill to use, and they can be acquired easily and cheaply on the Internet. Buying a set of bump keys gives a burglar the ability to open 95% of the deadbolts in the United States. But simply buying and installing bump-proof locks completely removes this threat.

Medeco high security deadbolts are one option. You can buy them here on Amazon.


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