The Smart Key on most Mazda vehicles allows you to sync to your engine to start your car; it also controls your door locks and boot release. You can program the MX-5 in just a few simple steps from your driver's seat. This programming sequence will allow you to sync up to three different keys.
Insert one key into the ignition. Turn it to the "on" position and press the "unlock" button on all of your key cards.
Cycle the key in the ignition from "acc" to "on" three times in succession. Open the driver-side door.
Press the "unlock" tab on the door twice. Close the door again and wait for the locks to automatically cycle.
Press the "unlock" button on your first card key. Wait for the locks to cycle again and then do the same with any additional keys. Remove the smart key from the ignition after the last card to finish the programming.