SAN JOSE, Calif. (McClatchy) — Remember those halcyon days of six months ago, when Amazon introduced a feature for its Prime customers called Amazon Key, which lets a delivery courier use the cloud to unlock your front door and put your packages inside your house?

Well, on Tuesday, Amazon said it will take that concept another step farther by unlocking and making deliveries to your car.

The new feature, which is available for its Prime members in 37 U.S. cities, uses the connected technologies that are being built into more cars these days. Amazon said Tuesday it has lined up General Motors and Volvo as the initial automotive partners to incorporate the delivery technology with their vehicles.

The way it works: Say you’re running out of diapers at home, but you don’t feel like stopping at Target on the way home. You can use the Amazon Key app to arrange for Amazon to come to your car, unlock it electronically, put that box of Pampers in your trunk, lock the car up and get a notification that the delivery was completed.

Amazon has been testing the service for the last six months in San Francisco and Washington state. Among Bay Area cities, the in-car delivery service is available in San Jose, Oakland and San Francisco. The company has a tool where people can plug in their ZIP codes and vehicle models to see whether the service is available in their areas.

There are a few caveats to the service. For now, it’s available only on select GM and Volvo automobiles made since 2015. A delivery has to be made within a certain radius for an address used by Amazon for deliveries, and, as the service is now just in 37 cities across the country, it isn’t everywhere, yet. In order to locate your car, the Amazon couriers will use the vehicle’s GPS location, license plate number and an image of the car in order to ensure they are making their delivery to the right auto.