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Why Bump Keys Don’t Work On Cars

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When I first found out about bump keys, it took me a while to feel safe again. It seemed like some universal key, that when used in conjunction with a hammer opens any lock. Of course, this is not the case. Bump keys may be quite easy to use, but they require some knowledge. Part of that knowledge is understanding the limitations of lock bumping. One of those limitations is automobiles. But why is is that bump keys do not work on cars? To understand why something doesn’t work it is necessary to understand how everything is supposed to work. For those of you who are new to some of this terminology, I will do my best to keep things simple. Beyond understanding why you cannot bump the locks on a car, we will discuss if it matters at all. Does having a bump resistant car really increase your security? What are some other methods that do work? How similar are they to a bump key? Are they easier to use? Let’s dive right in.

How a Bump Key Works

A bump key is most often associated with a standard pin tumbler lock. A very basic explanation of how it works requires a cursory understanding of a basic lock: A lock opens when the correct key is inserted, and stays locked if the incorrect key is used. This is because the correct key will orient the internal components so that bolts, locking dogs, etc. can be retracted. In the case of a basic pin tumbler lock, the lock uses several stacks of pins. In each stack, there is a key pin (bottom pin), a driver pin (top pin), and a spring (above the top pin). The key pins are varying lengths, the driver pins are a standard length (usually), and the springs are all similar (usually).

So now that we have the basic components, we need to know the basic parts of the lock. Very basically, there are two parts of a pin tumbler lock, the plug, and the bible. The plug is a cylinder that the key is inserted into, and the bible is the housing for that plug. When a key elevates the pins properly, the driver pins and springs will rest in the bible, and the key pins will rest in the plug. The line that separates the plug from the bible is called the shear line (remember that, it is important). Once the different pin types are separated by that shear line, the plug can rotate, and that will open the lock.

Key Terms

Key Pin – The bottom pins that the key touches directly. The key pins are different sizes. When the correct key is inserted, all of the key pins will rest in the plug.
Driver Pin – The top pins in the key stack that touch the springs directly. The driver pins are a uniform height. When the correct key is inserted, all driver pins will rest in the bible.
Bible – The housing for the plug. The bible will hold the driver pins and springs when the pins are at the shear line.
Plug – The plug has the keyway. It will rotate once the pins are at the shear line. When everything has reached the shear line, the plug will house the key pins.
Shear Line – The line that represents the boundary between the plug and the bible. When the lock opens, the pins are said to have reached the shear line.

Basically, what a bump key will do is move the pins to either side of the shear line for an instant. First, the bump key is placed in the lock. Put it all the way in, make sure it is touching all the pins. Pull it out one click. If you cannot hear the click, look for the beginning of the first groove closest to the bow (flat part that you turn with your thumb and index finger) of the key. Strike the bow of the key with a hammer as you turn the key in the lock. What this process is doing, is striking all of the key pins with enough kinetic energy to send the pin stacks flying up into the bible. The hope is that when you turn the key you will be turning it when the drivers are above the shear line and the key pins are below. Because this method relies quite a bit on luck, it helps to try it several times.

The key itself must be modified from a key that would fit the lock it is being used on. That means that a Schlage lock requires a bump key made from a Schlage key, a Kwikset lock requires a bump key made from a Kwikset key, an Evva needs an Evva, and on and on it goes. Once you have a key that will fit into your lock, regardless of whether it will open the lock, you can make a bump key. The only trick is making sure your key is long enough for the lock. Some brands will make five pin and six pin locks. If you have a key for a five pin lock, it may fit into the keyway of the six pin lock without reaching the last pin. Without manipulating all the pins in a lock, a bump key is useless. Also, the internal components will need to have a predecided direction to be moved. In this case, all of them are being moved up, because that is the only direction they can move.

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Key Take Aways

  • Bump keys are most commonly used in pin tumbler locks.
  • A bump key is used with a hammer.
  • Bump keys work on the principle of moving all of the pins to the shearline for a split second.
  • A bump key must be made to fit a specific type of lock.

How a Car Lock Works

Car locks do not use a pin tumbler system. When it comes to vehicles, in general, they will most likely use wafer locks or sliders. To tell what your car has, simply look at your key. If there is biting (the serrations that break from the smoothness of the key blade) on both sides then your lock uses wafers. If you have a very rectangular key with a kind of snake pattern engraved in it (usually on two sides) then your lock uses sliders. In either case, they are different from a pin tumbler lock.

Wafer Locks – This type of lock is by far the closest to a pin tumbler lock. How it varies is that one wafer is moved, instead of a stack of pins. These wafers must be elevated and depressed to a certain height. If they are not moved to the correct specifications then the wafers will bind at the shear line, keeping the plug from rotating.

Slider Locks – The snake-like path on the side of your key is going to move sliders within the lock. They act very similarly to wafers, and, as a result, are the natural evolution for the automotive industry. How they work is the path on the key will move the sliders either up or down, to a very specific place. Once all the sliders are aligned, this will allow the plug to rotate.

What would happen if you tried a bump key on a car?

If anything happens, it is going to be your lock and/or key breaking. When you strike the bump key with your hammer or hammer substitute, the top wafers (assuming the car has wafer locks) will jump. But unless you have made your own double sided wafer bump key (and you will learn below why it is unlikely anyone would waste their time on this), there will still be bottom wafers that remain unmoved. If the lock has sliders, then jolting the lock would do even less. An impractical amount of knowledge about the specific vehicle lock would be needed just to make an attempt at a functioning wafer lock bump key. If you were to try and move all the wafer simultaneously, then you need to know which are being moved up and which are being moved down. For sliders, this is not even an idea worth contemplating. There is no set point in the lock where you can move the sliders uniformly and open the device.

Keys That Will Work


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Jiggle keys are the vehicle equivalent of a bump key. In a way, they are the missing link on the evolutionary progression of security-undermining products. Jiggle keys go by other names: auto jigglers, tryout keys, etc. Then there are slight variations like Marshall keys and wave keys. They are all pretty much the same, but we will address the some of the finer distinctions. First, let us reset, and restate the knowledge we have gained thus far. Think back to the principle of a bump key. That key is trying to move the pins temporarily into position with one strike. Now let us think back to car wafer locks. We will disregard sliders for the time being because tryout keys only work with wafer locks. Therefore, this method will not work on all

Now let us think back to car wafer locks. We will disregard sliders for the time being because tryout keys only work with wafer locks. Therefore, this method will not work on all cars and will be entirely unaffected to most newer models. Back to the point, a wafer lock uses pin like mechanisms on both the top and bottom of the lock. We now understand that it is the double sided security that keeps a single hit from moving all the wafers to the necessary height. Well, the logical answer is that a key must be used that will manipulate both sides of the lock.

The basic tryout/jiggle key is placed in the lock and moved up and down vertically. This movement does not need to be rough. Slow and gentle should do the trick well enough. It is very similar to rocking a pin tumbler lock, except that you are not moving the tryout key back and forth from the back to the front of the lock. Also, there is no need for any tension tools, because the tool manipulating the wafers can also be turned to create tension you now have an all in one tool. These keys can work on door locks as well as ignition cylinders. Which can be solved by replacing the ignition cylinder with an upgraded model. As long as the ignition does not require a transponder chip, all you need to do is pick the lock. Though jiggling these keys is often the root of their functionality, there are instances where simply turning them like a key will work. Not all of the tryout keys will work on your locks. Most often there is one out of a set that works on a particular lock.

For more advanced locks you will need more advanced keys. This is where Marshall and wave keys come into play. These keys are cut with specific makes and models in mind. Certain wave keys will even have cuts to properly move sidebars. Ideally, these keys will work without being rocked in the lock, but they can also be used to rock and rake the lock (as turning pressure is applied). When they work without incident, you will simply turn them in the lock. Start with the first key in the set (appropriate for your make and model), and turn it in the lock. If it does not work, turn the key to the opposite side and try again, before moving on to the next key. Similar still to the tryout keys, not all of these keys will work.

Key Take Aways

  • There are key templates that will open vehicle locks.
  • Automotive tryout keys do not require a hammer.
  • In some instances, all you will need to do is turn the false key in the lock.

Why It Really Doesn’t Matter


From a security standpoint, none of this should be that alarming. Cars and other vehicles are ultimately insecure. With motorcycles, there are much more affordable bypasses for ignitions and locks. With cars, most can be opened with a chunk of wood and a stick. If a criminal is going to try and steal a car, and they are going to put some effort into learning a new skill, it makes sense to learn others. In the locksmithing trade, this is also true. For example, it would be much easier to get very proficient in wedging a door and opening it with a probe. This will work on pretty much any car and you can be in seconds. Compare that to the skill and time to open unique locks, each of which will need a slight variation in each opening procedure. The bump type methods of opening require too much trial and error for most people. Just because a lock cannot be bumped, it does not mean that the lock cannot be opened another way. Most people assume bump keys are the easiest method of entry, but there are simpler ways out there.


In the end, the most straightforward thing to say is that bump keys don’t work on car locks because they were not meant to. There are different keys meant to work on vehicles. That is right. Vehicles are not safer than a lock that can be bumped. Bump keys are a single attack. What good is a lock that can’t be picked if it can be bypassed? What is the use of having a padlock that cannot be cut if the core falls out when you hit it with a hammer? Security is about balance. It is about every attack in the book, being hard to pull off. The struggle is in keeping the difficulty diverse. It is more than fine to use any of the methods described in an emergency situation in areas where owning these tools is legal, as long as you are not using them for criminal behavior. The Lock Blog is a resource for honest citizens and security professionals that wish to know more about the finer points of the industry. Any and all use of the Lock Blog’s content for criminal activity is a violation of the content’s intended purpose. Please continue to be upstanding citizens, and stay safe.

Category: Automotive, Car Keys, Lock Picking, Tools of the Trade

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