How to use an iPhone as a car key? - According to the description of the CarKey interface, which was suggested by Apple itself, it will work passively and no active actions will be required from the user.
It will be enough to just go to the reading area, as the doors will be unlocked automatically, and the Start Engine button will allow you to start the car without taking the smartphone key out of your pocket. You don't even need to pass identification using Face ID or Touch ID. By the way, Express transport cards work in the same way, which do not need your biometrics to pay for public transport using your smartphone.
Interestingly, the process of pairing a smartphone with a car will be performed through the Wallet app. The user will first need to activate the reader function on the iPhone, and then place it in close proximity to the car reader. This is usually either the door handle or the dashboard. After that, Wallet will analyze the data sent by the machine and store it in the smartphone's memory for future use.