How Intruders Can Use Lock Bumping to Enter Your Home

Cylinder locks are quickly compromised with a bump key.
Irakli Abashidze/EyeEm/Getty Images

Lock bumping is a phenomenon that has been getting a lot of attention. Most homes still use cylinder locks as a main source of security, but these locks are easily compromised with a little know-how and a few basic tools. A technique known as "lock bumping" was first classified as a security concern around 2002. To bump a lock, a burglar inserts a specially cut key into the lock, then gently “bumps” it with a mallet or a screwdriver. This forces the pins in the lock to the shear line as the key turns and the door opens. The “bump key” required to accomplish this is simple to acquire and can even be ordered online. The technique requires no special skill and it's effective most of the time, allowing thieves to enter your home without any sign of forced entry. The potential for lock bumping is a real threat that you should take seriously when evaluating home security.

The History of Lock Bumping

Lock bumping is a technique that had been used by locksmiths for half a century when they needed to access a lock with no key readily available, but for most of that time, it was not a well-known criminal technique. The best-known method of violating a lock was lockpicking—a technique that takes time and requires specialized tools and training. The brute force to get around a lock with this method makes noise and leaves behind signs of a break-in. Lock bumping, on the other hand, is quick and relatively quiet.

The Bump Key

A special bump key is required for lock bumping to be effective. The key must be the appropriate size for the lock, but the only other requirement is that each ridge in the key is cut to maximum depth. People often refer to bump keys as “999 keys” because each ridge is cut to a depth of 9 in a key-making machine. These keys are therefore easy to produce and acquire, and they take less than five minutes to make. Older and cheaper locks are actually more resistant to bumping because they are not cut as precisely; they're clunkier and the internal pins don’t move as smoothly as on higher-end locks.

Lock Bumping Statistics

It is difficult to know how prevalent lock bumping currently is in home break-ins because it leaves no sign of forced entry and the lock continues to work normally afterward. Therefore, a burglar needs to be captured with lock-bumping tools in his possession or caught in the act to verify that lock bumping was used in a crime. Even when a break-in is verified, the lack of visible signs does not necessarily mean that lock bumping was the method used. Almost two-thirds of all break-ins do not show signs of forced entry, and many of these break-ins likely happen when criminals gain entry through an unlocked door or window or obtain a duplicate key through dubious means. Although difficult to quantify, lock bumping should not be discounted as a serious threat.

Prevention

The Internet is full of videos, articles, and instructions on how to bump a lock and methods that can be used to acquire the key needed to accomplish the task. Thus, you'll need stronger locks or additional security features to minimize risk:

  • Add chain latches to your exterior doors if you don’t have them already. This doesn’t affect your lock’s susceptibility to bumping, but it provides an additional barrier that a thief will need to bypass in order to gain entry.
  • Have a locksmith modify your existing locks and deadbolts by adding additional pins to them. This doesn’t make your locks immune to lock bumping, but it does make the process more difficult. This is usually more cost-effective than lock replacement.
  • Replace your existing locks with bump-resistant locks. The locks are typically much more expensive, but lock bumping won’t work on them. You can usually install the locks yourself if you want to save on installation fees. When buying a new lock, look for the grade assigned to it by ANSI (American National Standards Institute). The standard grade 3 locks, by far the most common in residential use, are fairly easy to open by lock-bumping techniques. However, grade 2 locks, which are commonly used in commercial applications and in apartment buildings, are regarded as quite resistant to bump keys, and they are often installed in ordinary residential applications. Grade 1 locks are top of the line, completely immune to entry from bump keys, and also virtually pick proof. These are the best choice where maximum security is desired.

While lock bumping is a genuine concern, your first priority should still be ensuring that all your doors and windows are locked at night and when you’re not home, as those points of entry still pose the larger security risk. Once you know your house is secured in this most basic way, consider ways in which to make those exterior defenses stronger. Talk to a locksmith about improving or replacing your existing cylinder locks and to learn what potential solutions fall within your budget.