In rekeying a lock, the locksmith removes the pins and springs in the lock cylinder and replaces them with new pins and springs that work with a new and different key. Unless a lock is malfunctioning or a totally different style is desired, many locks can be rekeyed and kept in service, operating as well or better than ever.

The most common reason to rekey the locks is to maintain key control when there is a change in possession of a property. Key control simply means accounting for all keys made to operate the locks. Once keys are loaned out, key control is lost. Obviously, with a previously owned home, you don’t know who may have had access to the keys. In new homes, contractors have had access to the keys.  

In many single-builder communities, locks are construction master keyed. While the use of the homeowner's key may prevent the future use of the contractor's key, there are often master pins left in the lock. Each master pin doubles the number of keys that will operate the lock. In many instances, as many as 16 different keys would operate a single home's locks. Rekeying would remove these master pins and eliminate the possibility of another key operating the locks.  In many instances, as many as 16 different keys would operate a single home's locks.

Rekeying allows a locksmith to examine the condition of the lock and its installation. Many problems can be corrected without replacing the lock. Locks are usually lubricated when rekeyed, which can make them operate much more smoothly. Then again, problems may be discovered that indicate that a lock should be replaced.

Some lock manufacturers are offering locks that can be rekeyed by the consumer. These are not the standard pin tumbler locks that have served as the backbone of the lock industry. To allow rekeying without disassembly introduces a lot of additional intricate parts that can lead to malfunctions and tend to be easier to bypass than traditional locks.