To start off most locks can be rekeyed. Rekeying is a process in which the lock is taken apart, the old pins which correspond to the current key are removed and new pins are installed that correspond to a new key. If you have two locks that use two different keys one can be rekeyed to match the other as long as it’s the same keyway. It’s a good idea to have locks rekeyed rather than replaced on a new move in if the hardware is of decent quality and has current keys to it as it’s typically cheaper. If it’s missing keys altogether it’s possible but more expensive as taking it apart becomes more difficult.
Keying alike is the process of making multiple locks work off of one key. For convenience all of the locks in a business or home can be keyed to one key. In the example below the front door, back door. Garage, workshop and office would all be opened by one key.
Master keying is the process of being able to key several locks differently but have one master key, or a key that can access every lock. In the example above if Dan wants the front door, back door and garage keyed alike so his family can get in the house while his workshop is keyed differently so employees can get in the shop and his office keyed differently so only he can get in its completely possible for him to have these locks keyed this way while also having a master key that can open everything.
In this example the family has a key for the house which allows access to the front and back doors as well as the garage. The Employees have a key the workshop and Dan himself has a master key that opens all of it. If one of his employees leaves only the shop doors need to be rekeyed to maintain security.