provided by: 
It happens all too often: a person moves into their new home or business and forgets to re-key the locks. I literally cringe when I'm called to a home or business and find out the locks have never been re-keyed. I'm talking about protecting, for the most part, your largest investment for a cost of under a hundred dollars.
Re-keying is not an expensive procedure and it usually only takes a few minutes to change several locks. Re-keying a lock should not be confused with replacing a lock. You do not need to replace the locks in your home or business to lock out the previous key.
A locksmith simply removes your existing locks and disassembles the lock cylinder (the area that accepts the key) and discards all the old pins. New pins are installed that match the new key and at that time the lock cylinder is inspected, tested and lubricated to assure that the key will turn smoothly. After completing this procedure the lock is then reinstalled back on your door, guaranteeing that the old key will no longer work.
It's important to act immediately when a house or business key is lost, just in case it falls into the wrong hands. A general rule of thumb is to always assume that it has fallen into the wrong hands, and that the finder knows your name and where you live or work.
When a theft occurs, law enforcement officers usually look for visible signs of entry. When a thief pries a door, they leave identifying marks on the door or doorframe. However, when a key violation occurs, through a lost or stolen key, there are no signs of forcible entry.
With no signs of forced entry, police officers and insurance companies naturally become suspicious and may ask such questions as: Did the intruder have a key? Did the homeowner negligently forget to lock one of his or her doors? Did the homeowner stage the theft? In some cases insurance companies may suspect foul play, causing them to be less willing to pay an insurance claim without further investigation.
Most homes have all their locks keyed alike. Having one key for all locks is very convenient and saves the frustrating task of locating the proper key to the proper lock. However, if you are concerned a family member may lose or misplace a key, it may be advantageous to have a designated door on a separate key for that family member to use. The benefit being, if the key is lost or stolen, you only have to re-key the locks on the designated door instead of all doors, keeping your re-keying costs to a minimum.