Rekeying is the process of changing a lock so that the old key no longer works, but a new key does, and supplying new keys that work smoothly. In the case of locks with pins, this involves opening up the cylinder, and changing out the pins. The indentations you see along the length of a key are in fact the sites and depths of those pins. On a standard residential key with five grooves, the locksmith is changing out five pins to fit the grooves on a new key. On smaller keys, like those for mailboxes or cabinet drawers, those four grooves along the length of the key correspond to the four pins or wafers within the cylinder.
Closely tied to the quality of repining, is the accuracy of key duplication. Locksmiths make use of factory cut original keys, cut very accurately to code, and then make duplicates of these factory cut originals. These duplicates are only as good as the key machines on which they are made, and the ability of the person who cuts them. The locksmith on the road has one great advantage over the person cutting keys in a shop or retail establishment. The person on the road can actually test the key on each cylinder that is rekeyed, as well as every other lock on the site which that key has to work on. This is a great advantage, because even with the very finest equipment, there are occasional blanks which are imperfect, don’t go into the cylinder easily, or are not cut carefully enough. Being able to actually test the key allows the mobile locksmith to present the customer with 100% accurate duplicates.
Although the overwhelming majority of residential and commercial keyed locks contain pins, and are thus readily rekeyable, the two largest manufacturers, Schlage and Kwikset, have brought out residential locks over the last year or so which do not contain pins. They have done so, presumably, to counter the use of bump-keys, readily available on the internet, which can be used to pick pinned locks. A bump key is in fact a low cut key which acts as both a pick and a tension wrench in the form of a specially cut key. When inserted into the cylinder, and given a bit of rotational pressure, the bump key, when struck with a hard object, does the same thing as a pick and tension wrench. It bounces the pins within the cylinder, allowing the creation of a sheer line, and the cylinder turns. Unpinned locks may be here to stay, but they are a work in progress, with a host of mechanical and engineering faults. First of all, they have been almost universally rejected by locksmiths and the wholesalers who supply them. This is not only because they are not repinable, but because they are easily defeatable, and prone to failure in the rekeying process. One needn’t be a cynic to suspect that Schlage and Kwikset perhaps hope to boost, extravagantly, their sale of residential locks by feigning provision of a bump-proof lock, which is in fact, basically non-rekeyable. Harsh, but true. Think Wall Street, cheater loans. Over the mid-term, purchase locks which contain pins, or better yet, high security locks.