The trajectory of evolution of modern automobiles allows anyone to argue that cars are no longer just mechanical tools for transport but have become distributed computing platform on wheels, making almost all systems related to typical automobiles obsolete. 

It is easy to see that what used to be a simple mechanical interface is now expected to operate within a system defined by connectivity, software control, and dynamic user identity.

Older vehicles are simple mechanical systems that are complimented by simple electrical systems operating as an independent, isolated automobiles 

Modern vehicles have become so complex that they closely resemble computers more than they are cars. Internal systems within modern vehicles are controlled by numerous electronic control units (ECUs) with diverse functions that include, but are not limited to, adaptive cruise control, automatic emergency braking, lane departure assist, and blind spot detection, to name a few. 

This means that functionalities typical in older vehicles no longer apply for the more modern ones. This includes car keys. 

Traditional keys offer dual or binary functions - to lock/unlock the car door and to start the engine. Mechanical keys, transponder keys, remote key fob, and proximity keys are considered traditional keys even though there are electronic circuits integrated in them in the sense that these are physical objects carried around. 

Modern Vehicle keys implement the Phone-as-a-Key (PaaK) feature where one's phone acts as the security ID for the vehicle to allow the holder of the phone to lock/unlock the vehicle when the phone is in close proximity to the vehicle, start the engine, and access all the features of the vehicle. 

Below is a side-by-side comparision between traditional keys and Phone-as-a-Key systems.