Auto locksmiths work with two different types of car keys. The first are car keys that are not linked to a fob or an electrical component. These are fairly simple to make and are not differ to obtaining a duplicate house key from a typical residential locksmith.
When it comes to car keys that are attached to a fob, things get a little more complicated. Many of these keys are also transponder keys, which means they have a chip that is unique to that vehicle.
The car will not start unless the ignition reads the code stored in the chip. You can have an auto locksmith duplicate just the key portion of the key fob; however, if it's a transponder key, it's a little more complicated.