Don't get bumped!
As a working locksmith, in business now for over 25 years, I am trained in various techniques generally referred to as "lock picking". Knowing how to defeat locks without damage is one of the fundamental skills expected of anyone in this industry. For the most part, lock picking is an art when it is practiced using conventional tools. Like so many other skills, it can be taught to pretty much anyone who has the desire to learn, but it takes practice and real skill is not acquired quickly. It is for these reasons that very few run of the mill burglars enter homes or businesses by picking the locks. They use faster and usually more destructive techniques.
However, though the technique is not new, a practice known as "bumping" or "key bumping" is enjoying new popularity thanks largely to the Internet. This is actually a legitimate form of lock picking and can often succeed in opening locks that resist other more mainstream picking techniques, and it is one that requires no special tools. It is capable of giving reasonably quick entry through a locked door without damage and with little noise, thus posing a real threat to the security of your home.
The intent of this article is not to provide a primer on key bumping, but to provide ideas that will go a long way toward protecting the public from its unauthorized use. In order to do that, I think it is important that the reader acquire a bit of understanding of how the technique works.
Key bumping works best on pin tumbler locks, and that is exactly what you have on the doors to your home and business. Pin tumbler locks have long been the standard in door hardware as they provide higher security than do locks making use of disc tumblers, also known as wafer tumblers. Most residential locks have 5 pin tumblers whereas 6 is the norm for commercial and industrial hardware.
When a correctly cut key is inserted into a lock, the tumblers settle into the bittings of the key. Those are the low points, or valleys, in your key. Contrary to popular belief, the tumblers are aligned by these low spots and not by the "peaks" or high spots on the key. The tumblers and the key are matched so that when the key is fully inserted all the tumblers form a shear line -- which means they all line up in a straight, flat line inside the lock which allows the key to turn the lock. When key bumping is used, a key is inserted in which all the bittings have been cut down to the deepest measurement permissable for the specific kind of lock involved. Naturally this makes all the tumblers drop too far inside the lock and there is no shear line . . . yet.
Key bumping comes into play when this fully inserted special key is rapped, or bumped, using a small mallet or even a piece of wood. As the key is bumped, a slight amount of turning pressure is applied to the key. Bumping rhythmically causes a percussive effect inside the lock as energy is transmitted from the key to the pin tumblers that have settled into its bittings. The tumblers begin to jump upward and then fall back down, repeatedly, and eventually there will be an instant in which all of the tumblers have found themselves at exactly the right level within the lock to form the necessary shear line. Because there is always just a hint of turning pressure being applied to the key (this is also varied rhythmically as the bumping is carried out), the lock will turn at that instant and the door is unlocked.
Because this technique is so easily learned, and because the specially cut keys are not at all hard to come by (they can be purchased from hobby sites and locksmith supply sites), key bumping has been growing in popularity with that portion of society you would rather not have it . . . burglars. So what can we do about it? Here are a few good suggestions:
Make certain your exterior doors are protected by at least two keyed locks . . . one keyed knob or lever and a deadbolt. This will at least require that any would-be burglar will have to defeat two locked cylinders instead of one.
Change out your residential-type 5-pinned deadbolts for commercial models that make use of 6 tumblers. They are always better quality, they have tighter tolerances, and the extra tumbler makes them much harder to pick no matter which technique is used.
A constrictive keyway such as found on Schlage locks is preferred to the wider keyways of Kwikset, Weiser, Yale, and other manufacturers. It is well known that Schlage keyways are harder to defeat by bumping than are most others.
The single most effective security measure, and likely the least costly, is to bathe your entry doors with light during nighttime hours. I suggest the use of floods with motion sensors for low cost and efficiency.
All these measures do more than just protect you from "getting bumped." They are equally effective at dissuading other types of crime and they will give a heightened sense of security and well being. Remember, you are protecting more than just real estate!
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