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Lock bumping

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Title: Lock bumping  
Author: World Heritage Encyclopedia
Language: English
Subject: Lock picking, Locksport, Locksmithing, Disc tumbler lock, Magnetic-coded lock
Collection: Locks (Security Device), Locksmithing
Publisher: World Heritage Encyclopedia

Lock bumping

A typical bump key

Lock bumping is a lock picking technique for opening a pin tumbler lock using a specially crafted bump key, rapping key or a 999 key.[1] A bump key must correspond to the target lock in order to function correctly.[2]


  • History 1
  • Mechanics 2
  • Use by criminals 3
  • Countermeasures 4
  • References 5



  1. ^ Graham Pulford (17 October 2007). High-Security Mechanical Locks: An Encyclopedic Reference. Butterworth-Heinemann. pp. 76–.  
  2. ^ a b Lock Bumping and Bump Keys. YouTube. January 18, 2007. Retrieved November 7, 2012. 
  3. ^ a b High Security Mechanical Locks - An Encyclopaedic Reference published by Graham W. Pulford 2007, p. 19
  4. ^ Marc Weber Tobias (August 24, 2006). "The Lockdown: Locked, but not secure (Part I)". Retrieved January 8, 2015. 
  5. ^  
  6. ^ Barry Wels; Rop Gonggrijp (January 26, 2005). "Bumping Locks" (PDF). Toool - The Open Organization Of Lockpickers. Retrieved June 22, 2009. 
  7. ^ The Lockdown: Locked, but not secure by Marc Weber Tobias. Retrieved February 12, 2007.
  8. ^ "Lock Basics and Mechanical Operation". Toool. Retrieved August 8, 2012. 
  9. ^ Pick a Lock in SECONDS with a Bump Key - Scam School. April 14, 2010. Retrieved January 8, 2015. 
  10. ^ "Understanding Bump Keys (Video)". L. Scott Harrell. 19 Apr 2009. Retrieved Oct 1, 2015. 
  11. ^ Steve Irvin (2014-05-06). "Is your home at risk? Lock-picking dangers, ways to protect yourself". ABC15 News. 
  12. ^ "WATCH: The 3D-printed 'bump keys' that can open almost ANY lock in seconds". Jonathan O'Callaghan. Daily Mail. 1 September 2014. Archived from the original on June 22, 2015. Retrieved Oct 2, 2015. 
  13. ^ "Statistical bulletin: Crime in England and Wales, Year Ending March 2015". Office for National Statistics. Retrieved October 2, 2015. 


Changing the spring tension can help reduce bumping. A few sources inside the industry offer stronger top springs for conventional pinned locks. changing one or two top springs to a firmer spring changes the ricochet tuning of the top pins, making it hard to bump.

Time locks, combination locks, electronic locks, magnetic locks, and locks using rotating disks, such as disc tumbler locks, are inherently invulnerable to this attack, since their mechanism does not contain springs. However, some electronic locks feature a key backup that is susceptible to bumping. Warded locks are not vulnerable to bumping, but they are vulnerable to a similar attack called a skeleton key, which is also a filed-down key.

Locks that only use programmable side bars and not top pins are bump proof. BiLock is an example of this technology. Many bump-resistant locks are available which cannot be easily opened through the lock bumping method.

Locks that have trap pins that engage when a pin does not support them will jam a lock's cylinder. Another countermeasure is shallow drilling, in which one or more of the pin stacks is drilled slightly shallower than the others. If an attempt is made on a lock that has shallow drilled pin stacks, the bump key will be unable to bump the shallow drilled pins because they are too high for the bump key to engage.

Because a bump key must only have the same blank profile as the lock it is made to open, restricted or registered key profiles are not any safer from bumping. While the correct key blanks cannot be obtained legally without permission or registration with relevant locksmith associations, regular keys can be filed down to act as bump keys.

Locks having security pins (e.g. spool or mushroom pins)—even when combined with a regular tumbler mechanism—generally make bumping somewhat more difficult but not impossible.

High-quality locks may be more vulnerable to bumping unless they employ specific countermeasures. More precise manufacturing tolerances within the cylinder make bumping easier because the mechanical tolerances of the lock are smaller, which means there is less loss of force in other directions and mostly pins move more freely and smoothly. Locks made of hardened steel are more vulnerable because they are less prone to damage during the bumping process that might cause a cheaper lock to jam.


Lock bumping is a recent trend in burglaries,[11] which can make it easy and fast to break into homes without needing too much special equipment or leaving any trace of forced entry. It works almost as well as actually having a key,[2] and a set of 10 rapping keys can make the criminals capable of opening 90% of common tumbler locks. However, criminals might choose to avoid lock bumping when stealth is required, because of the noisiness of the process. Almost all tumbler locks are vulnerable to bumping.[12] In the UK, recent trend of break ins using the front door as the entry point has reached 73% according to the office of National Statistics.[13]

Use by criminals

A different tool with a similar principle of operation is a pick gun.[3]

When bumping a lock, the key is initially inserted into the key way one notch (pin) short of full insertion. Bumping the key inward forces it deeper into the key way. The specially designed teeth of the bump key transmit a slight impact force to all of the bottom pins in the lock. The key pins transmit this force to the driver pins; the key pins stay in place.[10] This physics action can be visualized by observing the same effect on the desktop toy: Newton's cradle. Because the pin movements are highly elastic, the driver pins "jump" from the key pins for a fraction of a second, moving higher than the cylinder (shear line of the tumbler), then are pushed normally back by the spring to sit against the key pins once again. Even though this separation only lasts a split second, if a light rotational force is continuously applied to the key during the slight impact, the cylinder will turn during the short separation time of the key and driver pins, and the lock can be opened while the driver pins are elevated above the key way. Lock bumping takes only an instant to open the lock. The lock is not visibly damaged, although the force of the bump can leave an indentation on the front of the cylinder. Certain clicking and vibrating tools designed for bumping can also be used. These allow for rapid repetition of bumping against locks that have advertised "bump proof" features. Only a rare few key-pin locks cannot be bumped.

A pin tumbler lock is composed of a series of spring-loaded stacks called pin stacks. Each pin stack is composed of two pins that are stacked on top of each other: the key pin, which touches the key when it is inserted, and the driver pin, which is spring driven. When the different length key pins are aligned at their tops by the insertion of the correspondingly cut key at their bases, the tops of the key pins and, consequently, the bases of the driver pins, form a shear line, so that the cylinder can be turned, rotating the key pins away from the driver pins. When no key or the wrong key is in the lock, pin misalignment prevents the cylinder from turning.[8][9]

In a pin tumbler lock, when the correct key is inserted, the gaps between the key pins (red) and driver pins (blue) align with the edge of the plug, called the shear line (yellow).


Marc Tobias, an American security expert, began to talk publicly in the United States about the technique and its potential security threats. In 2006, he released two further white papers regarding the technique and its potential legal ramifications.[7]

A patent exists for a lock device following the same principle as the bump key from 1926–1928. [6]

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