Operating car with a key

In former cars, I would make extra copies of the key and keep them in case I locked myself out of my car.  With the smartlock system, I'm a little confused.  I know I can make extra keys -- but can they only be used to unlock the door?  I don't see a place to use the key to start the car (only the smartkey).  How much do the extra "smartkeys" cost.  I sorta hate the idea of giving a valet parking attendent the smartkey.  You can see I'm confused about this whole system......