Many old houses have beautiful internal locks on doors, but it many cases these keys have been lost over the years. Luckily, it's relatively easy to get new keys cut for these locks, and in many cases, all of the house locks will be keyed alike so a single key should work throughout the home.
Here are the steps involved.
Remove the locks
The locksmith will come to the house and will usually remove a lock. They will look for identifying information on the size and model of the lock in order to select an appropriate blank key. The locksmith then works on adjusting the length of the bit to the lock depth and examines the internal bolt of the lock to work out the shape of notches that they need to cut. They incrementally trim the key until it fits in the lock (as well as testing in the other locks). Once you have a working lock you can return the lock to the door.
Work the locks
Once a suitable key shape has been found, the locksmith will then try it in all of the locks in the house. If it is an old house and some of the locks have not been used for a long time they may require some additional maintenance to be able to move freely, including greasing the lock or replacing snapped pins. A professional locksmith can often work out simple solutions to old lock problems and advice on how to maintain the locks (such as regularly applying graphite solution). Older locks tend to be more vulnerable to corrosion and sticking as they are made of iron and steel rather than modern alloys such as stainless steel.
Get a spare cut
Now that you have working door locks and a new key, it's a good idea to get a spare key cut as well and kept in a safe location. That way you won't have to go through the same process again. Internal door keys in older houses are often quite chunky and don't sit well on modern key rings so you may want to search for a key hook or convenient drawer instead.
If you have some old locks in your home that you can't use due to the lack of a key, why not call a locksmith and get a new key cut? It's an easy way to restore your home's original design and function.