Amazon’s popping up everywhere, even in the back seat of your car. The online retail behemoth today announced it’s bringing the Amazon Key in-home delivery service to vehicles—even when people aren’t in them. Convenient? Yes, but also a little scary.

Below, a closer look at the service being branded as Amazon Key In-Car:

How does it work?

Prime members (which number more than 100 million, according to the Seattle-based brand) can download the Amazon Key app and link it with Amazon’s car service account to register the vehicle. When consumers are ready to purchase, they select “in-car” at checkout rather than delivery to a home or office location. They’ll also receive notifications regarding the delivery time and can track the locking and unlocking of the car through the app.

Who can use it?

For now, anyone who has a 2015 or newer Chevrolet, Buick, GMC or Cadillac with an active OnStar account, or a 2015 or newer Volvo with an active Volvo On Call account. The service will initially roll out to 37 cities and surrounding areas.

But I have a Subaru…

Amazon says more car brands and models will eventually be added to the offering.

How does stuff stay safe?

Amazon described it as a “one-time unlock” process, meaning the delivery driver gets access to the whole car, but only once for the delivery. Amazon says it uses “multiple layers of verification to ensure the security of in-car deliveries” including using an “encrypted authentication process” to ensure the delivery driver is at the right location with the right package. Customers get a notification once the delivery is complete and the vehicle is re-locked. Amazon says “no special codes or keys are ever provided to delivery drivers.” The retailer also says the program is covered by its “Amazon Key Happiness Guarantee,” meaning that consumers can file a claim if they discover any damage.

What’s in it for Amazon?

The new offering is yet another way for Amazon to ingratiate itself with consumers by eradicating any potential obstacles in the delivery process. The service might be good for consumers who fear package theft from their doorsteps or the notion of a delivery person in their homes, for example. If the roll-out goes well and more cars are added, it could strengthen Amazon’s brand with shoppers.

What’s in it for auto brands?

Quite simply, it’s no longer good enough to just sell a car. With competition coming from ride-hailing brands like Uber, automakers must keep adding value in the form of new services. Volvo today touted Amazon Key In-Car as part of a growing array of digital consumer services that already includes programs that allow drivers to send calendar-based navigation destinations directly to their cars; find nearby gas stations; and get help finding their car in large parking garages. Volvo began offering in-car delivery in parts of Europe in 2015.

“This mix of car and commerce is starting the next wave of innovation,” Atif Rafiq, chief digital officer at Volvo Cars, said in a statement, “and we intend to be at the forefront.”