Amazon Key's in-home delivery is all well and good (assuming you trust it in the first place), but there's an obvious caveat: you have to go home to get your package. Now, you might not even have to go to that trouble. Amazon has launched a Key In-Car service that, as you can guess, lets couriers deliver packages to the trunk of your vehicle as long as it's in a publicly accessible parking space. You'll need a 2015 or newer GM-made or Volvo car with an internet-savvy account (OnStar or Volvo On Call), but after that it's relatively seamless: the delivery driver requests access to your car, and you'll get a notification when the package has been dropped off and your car is relocked.
Crucially, the driver never gets a special code or key, so they won't have access to your vehicle beyond a given delivery. Amazon also checks that the driver is in the right location and carrying the right package. You shouldn't have to worry about a malicious driver using this as an excuse to swipe your ride.
The service is live for Prime subscribers in 37 cities around the US, and doesn't carry an extra charge. As with existing options like Key and Prime Now, Amazon isn't shy about its strategy here: it wants to be the fastest and most convenient option for your orders, particularly when you can't be home. And there's plenty of competitive pressure to do this -- Walmart has been speeding up its own delivery process, and it won't be surprising if in-car deliveries quickly become more than a novelty.