Juli Clover, writing for MacRumors last week:
watchOS 6.2.8 introduces Car Key, a feature also available on the iPhone with iOS 13.6. Car Key is designed to allow an iPhone or an Apple Watch to be used in lieu of a physical key to unlock an NFC-enabled vehicle.
Car Key needs to be implemented by car manufacturers to function, and BMW is one of Apple’s first partners. BMW’s Digital Key for iPhone feature will let iPhone owners tap to unlock their vehicles, start the car by placing the iPhone in the smartphone tray, place limitations on young drivers, and share keys with up to five other users.
Car Key will work in a wide range of BMW models, including the 1, 2, 3, 4, 5, 6, 8, X5, X6, X7, X5M, X6M and Z4 if manufactured after July 1st 2020. An Apple Watch Series 5 or newer is required, as is the watchOS 6.2.8 update.
BMWs are not the most expensive iPhone accessory you can buy — that would almost certainly be a Koenigsegg, and I suppose I could find time to test its CarPlay integration if anyone wants to lend me theirs. Car Key does seem to be the culmination of the smartphone as an ultimate convergence device, though. If you live in one of the handful of places worldwide that accepts a digital driving license, you have smart locks on your doors, and you have a BMW made in the last three weeks, you could leave home with nothing more than your iPhone. Sure beats the gigantic key fobs that most cars use.
This is the kind of thing that necessarily needs a lot of time to roll out. But, perhaps the next time you buy a car, this feature will be present and just work for you.