Saves on locksmith labor.

@Tina Lee good suggestion by @Nathan G. if you are DIY and have less than 20-30 or so doors.Unfortunately, the system he suggests gets cumbersome to manage at a certain scale.We've been using locksmiths for ages and here is how they do a master system:MASTER KEY- can have as many SFR doors you want under the master-MUTLI-FAMILY: can then add another layer of submasters, so you have a key that only opens every door in the building---Great for apartment type buildings where tenants often have a key for building entrance and another for unit entrance.

My Dad was an ice cream man and locksmith among other things.

@Justen Ashcraft   A locksmith is the easiest but I would check the windows and other doors first.

In my experience a locksmith can get into most locks.

What other steps needed before walking to the house with a locksmith to change locks.