Do not try to guess what it really means. Because for instance there are a variety of different kinds of SMART KEYS. Not only as you describe. Smart Key as Smart Phone or smth Smart means only that this device can 'make decisions' and/or perform rather complex functions which look like human ones. In other words this device let you free from doing something and even thinking about this and 'makes decision' to do this for you and 'does' this for you.
Concerning in-mold substrate this can be a kind of surface covering for instance a decoration. May be this is a special surface which is the key itself. That means that the surface is controlled by a lock and the lock opens only if the surface is identified.
Give me please the topic of the text and a part of the text around the words mentioned by you.
Student or Learner