An experienced locksmith will be able to make you a spare key even if you don't have the original one. When you contact a locksmith, you'll need to provide some information to the company before the key can be replaced. A well-trained locksmith can create a key without having the original one. How is that? Well, locksmiths have specialized tools and equipment that allow them to produce an exact copy of their old key, and they can do it in a variety of ways.
A tripwire is a curved tool that every locksmith must have for any job. It is mainly used to open frozen glasses (the pins inside a door lock align perfectly with the key made to open it).
While Do Not Duplicate keys are not considered restricted keys, there are some keys that locksmiths call restricted. It is possible that these types of keys cannot be duplicated due to duplication rights of the original manufacturer.