Lock bumping, also known as key bumping, is a lock picking technique that uses a modified key called a “bump key” to quickly and easily unlock a pin tumbler lock.
This is done by violently forcing the bump key into the keyway and “bumping” the internal pins above the lock’s shear line, allowing the key to turn and open the lock.
Now that’s a mile-high description of how lock bumping works, but in this guide, we’re going to tear it all down to the nitty-gritties and look at how bump keys work to open locks.
Then we’ll look at some of the countermeasures that make lock bumping more difficult—if not impossible.
Let’s get to it!
Table of Contents
History of Lock Bumping
The first known version of the bump key was patented by Hiram R. Simpson in 1928, which he called the “rapping key,”—as seen in the image at the bottom of this section.
Knowledge of the bump key remained a well-guarded secret of the locksmith trade until the early 2000s when Klaus Noch recognized it as a massive security threat to anyone using a lock to protect themselves and their possessions.
Since then, the knowledge and fear of lock bumping exploded, and as a result, a new generation of locks featuring anti-bump characteristics was born.
Fast forward to today, and you’ll find that lock bumping is still a very viable option used by locksmiths, hobby lock pickers, and on rare occasions, criminals.
What Is a Bump Key?
So what exactly differentiates a bump key from a regular key?
The magic behind how bump keys work is derived from its unique bitting.
The bitting of a key is essentially the “bits” cut out of the key's blade.
These cuts can be made at various depths, often expressed with a number between 0 and 9 on a key machine. Zero typically being the shallowest cut, while nine being the deepest.
What separates the bump key from regular keys is that all of the cuts are made to the maximum depth of 9.
This is also why bump keys are often referred to as “999 Keys.“
As you can see from the image above, this creates very short and sharp teeth on the key. When rammed into the lock, these little teeth will rapidly jolt the pins causing them to move towards the shear line. We’ll learn more about how the bump key works in a moment.
While these maximum “cuts” are the defining characteristic of a bump key, there is also one more thing you need to consider.
A bump key is specific to a particular lock and keyway and is not one size fits all. This means that whatever lock you are trying to bump, you will need a key or key blank that fits that lock’s keyway.
To bump a Schlage, you will need a Schlage key. To bump a Kwikset, you will need a Kwikset key.
And if you desire the ability to bump a ton of different locks, you're going to need a big keychain.
That’s it! Now let’s look at how the bump key works to open a lock!
The two required characteristics of a useable bump key are:
1. All cuts are made to the maximum depth.
2. The key fits the specific keyway you desire to bump.
How Do Bump Keys Work?
To fully grasp how lock bumping works, we need to briefly cover two things.
Firstly, we need to look at the parts of a pin tumbler lock to understand exactly what a bump key is accomplishing within the lock.
Secondly, we need to understand Newton's third law of motion and how it applies to bump keys.
After that, we'll throw it all together and look at how lock bumping works!
Understanding The Pin Tumbler Lock
There are 6 vital parts of a pin tumbler lock that are important to know regarding lock bumping.
- Cylinder: The stationary part of the lock that “houses” the other internal components.
- Plug: A smaller cylinder that rotates within the main body cylinder. It also contains the keyway.
- Shear Line: The physical gap between the inside of the cylinder and the outside of the plug. Represented by a green line.
- Key Pins: The lower pins (red) that make contact with the key. Varying heights that match the correct key bitting.
- Driver Pins: The upper pins (blue) restrict the plug from turning by blocking the shear line.
- Springs: Force the pins into the plug and help the key pins read the cuts of the key.
To fully understand how all these pieces work together, let’s insert the correct key into a lock and see what happens.
When the key is inserted fully, the key pins fall into the cuts.
If the depth of the cuts and the height of the key pins match correctly, the driver pins will be removed from the plug.
Additionally, the gap between the key pin and the driver pin will match the shear line, thus removing the obstructions and allowing the plug to rotate freely.
Simply put, the goal of lock bumping is to remove the driver pins from the plug while keeping the key pins in the plug.
But how does a bump key accomplish this?
Newton’s Third Law of Motion
Bump keys work by exploiting Newton's third law of motion.
“When two bodies interact, they apply forces to one another that are equal in magnitude and opposite in direction.”
To understand how this is relevant, let’s look at a device called Newton’s cradle.
When the ball swings down and strikes the first ball in the stationary row, the moving ball will transfer its energy into the first stationary ball.
That energy transfer will continue through the remaining balls until the final ball receives that energy and swings outward.
What is important to note is that the center balls do not move. Rather they transfer the energy and remain stationary.
This principle can be applied to bump driver pins out of the plug.
How Lock Bumping Works
Okay, so how can we use a bump key and Newton’s third law of motion to open a lock?
To find out, let’s break down the entire process of bumping a lock.
We first insert our bump key fully into the keyway and then pull back one cut—or that is, until we hear the rearmost pin in the lock drop.
Next, with our bump hammer, we’ll hit the head of the key, jolting it forward into the lock.
The key's teeth will strike the key pins and transfer their force into the key pins—whose only direction to travel is directly away from the key.
However, because the driver pins are held snug against the key pins by the spring, that force will transfer from the key pins to the driver pins.
Like Newton’s cradle, this energy transfer will launch the driver pins away from the key pins.
If hit hard enough, the driver pins will leave the plug entirely, and if we are applying a turning force to the key while the driver pins leave the plug, there will no longer be any obstruction to the shear line, and the key will turn fully, and the lock will open.
How to Prevent Lock Bumping?
Lock bumping can be a terrifying thought to any homeowner, but it doesn't need to be.
There are some things you can do to make your locks more bump-resistant and better your overall security.
This topic deserves its own guide, but for now, I’ll cover the basics here.
1. Layer Your Security
The more obstacles that you put between what you want to protect and a criminal, the better.
You don’t need to live in Fort Knox or have 20 security devices guarding your front door to sleep soundly at night. Most times all you need is one or two additional obstacles to thwart most criminals.
Most burglars and lowlives don’t wish to spend a lot of time at the scene of their crime. They want in and out as quickly as possible and every second that they spend trying to get in is another second closer to being caught.
This is typically why criminals don’t pick locks. Most gain entry through brute force or through already unlocked doors and windows.
So by adding additional layers of security, you are increasing any criminal's chance of getting caught.
These layers can come in many forms, including additional locks, deadbolt guards, or door jammers.
A portable device that I personally use every night is the Buddy Bar Door Jammer. Unless they hit your door with a truck, they are not getting in.
For some other ideas, check out my article on ways to lock a door without a lock.
2. Add Security Pins
Modifying your existing locks is an effective and cheap way to upgrade the security of your locks.
One such method is by adding security pins to your locks.
Security pins are special pins that are designed to snag at the shear line if they are lifted while under tension—such as while turning a bump key.
Below is an example of a spool-type security pin.
Security pins won’t make your locks 100% bump-proof, but they will make it more difficult.
3. Upgrade Your Locks
The last option is to upgrade your security to high-quality bump-resistant locks.
For options that will work best for your situation, consider consulting a locksmith and have them set you up.
Installing locks may seem like a simple task, but if not done correctly can leave some major holes in your security that you won't be aware of.
If you're going to spend the money, you may as well ensure it is done as well as it can be.
Where Can I Buy a Bump Key?
Like most lock picking tools, bump keys can be found at every corner of the internet.
They are 100% legal to own in most locations, including 90% of the United States. If you live in the US, consider checking out my lock picking tool legality guide to find your local laws regarding bump keys.
You can buy bump keys from most lock picking tool brands, and I even sell them here at Art of Lock Picking. You can find my selection of bump keys here!
Additionally, you can make your own bump keys using a triangle file and any key blank that fits the keyway you are trying to bump.
FAQ: Frequently Asked Questions
How Effective Are Bump Keys?
Lock bumping is extremely effective and can bypass nearly 90% of locks used today. It is also a subtle form of bypassing that can be undetectable—meaning you may never know your lock was compromised.
Does Bumping a Lock Damage It?
While lock bump is a subtle means of bypassing a lock, it is still rather violent. Locks are built to withstand the simple forces of normal use. Hammering a key into the keyway is not "normal use" and could break a component—such as a spring.
How Long Does It Take To Bump a Lock?
The time it takes to bump a lock depends on many factors, including the type of lock being bumped and the skill of the lock picker. It can vary between a few seconds to never getting it open at all. But to give an average, the majority of locks can be bumped in under 30 seconds.
Bump keys are a genius lock picking tool that can quickly and simply defeat a huge majority of locks.
While they are a wonderful tool for locksmiths and blissful joy for hobby lock pickers, they can also be a dangerous tool in the hands of the malicious.
But by simply being aware of their existence and understanding how they work, you can do a lot to protect yourself from them.
After all, true security is understanding the flaws in your defense.
I hope you enjoyed this guide on lock bumping, and if you would like to learn more about lock picking and security, consider checking out my Academy for more free guides. Also, be sure to drop by the Art of Lock Picking shop for all your lock picking tool needs!