Re-keying a lock is the process of replacing the tumblers (pins, wafer tumblers) of a lock cylinder with new tumblers of different sizes. A new key will coincide with the new tumblers and the old key will no longer work. In other words, it is not necessary to buy new locks. Re-keying locks is something that should be done if you have moved into a new residence or lost a set of keys. Most automobile locks can be re-keyed as well. Re-keying locks is usually significantly less expensive than replacing them and just as secure.

Re-key your locks if you have moved into a new location had an employee leave had your keys stolen had contractors at your facility.
Even if you get your keys back from previous owners or former employees, it's easy for them to have duplicated your keys...and be able to gain access to your property, files, and cash.  

I just moved - should I re-key my locks even though they are working properly?
The answer is YES! Everyone gives their house keys to someone they trust. This does not mean YOU can trust them. How many neighbors, old baby sitters, cleaning people are walking around with the key to your home? Change the locks and then give keys to people you and you alone trust.