Last year, Amazon asked for permission to unlock your front door so it could leave packages inside your home, and a certain number of extremely trusting Amazon Prime subscribers (Amazon won’t say how many) said okay. Now, the tech giant wants to do the same thing with your car.

Amazon announced today a new service that gives its couriers access to a person’s vehicle for the purpose of leaving package deliveries inside. But rather than use smart locks and a cloud-connected camera to gain entry, Amazon wants to use the connected technologies embedded in many modern vehicles today. The company is launching this new service in partnership with two major automakers — General Motors and Volvo — and will be rolling out in 37 cities in the US starting today.

“We were really happy with the response to in-home delivery,” Peter Larsen, vice president of delivery technology at Amazon, told The Verge. “What we wanted to do — and it was part of the plan all along — is how we take that beyond the home.”

Amazon has been beta testing the new service in California and Washington state for the past six months. In a video by Amazon, a woman said she likes getting diapers delivered to her car because it meant her toddlers could nap without being disturbed by the doorbell. Another woman used it to have a few birthday presents delivered to the trunk of her car so as not to tip off her daughter.

To start out, the service will only be available to Amazon Prime subscribers. It’s also limited to owners of GM and Volvo vehicles, model year 2015 or newer, with active OnStar and Volvo on Call accounts. Amazon says it plans to add other automobile brands over time. Packages that weigh over 50 pounds, are larger than 26 x 21 x 16 inches in size, require a signature, are valued over $1,300, or come from a third-party seller also are not eligible for in-car delivery.

Amazon signed a two-year contract with GM and Volvo, a source with knowledge of the deal told The Verge, and all three companies have agreed to use these two years as a trial period. Neither the automakers nor Amazon hope to make additional money with the service, but instead saw it as an added convenience they can market to their customers, the source added.

To access the new delivery service, you need to add your car to your Amazon Key app and include a description of the vehicle, so Amazon’s couriers will be able to locate it. The car will need to be parked within a certain radius of an address used for Amazon deliveries, so either home or work. Driveways, parking lots, parking garages, and street parking are all eligible locations, just as long as it’s not at some random address across town.

Last week, The Verge got a demonstration of the new service from Amazon. After purchasing an item and selecting in-car delivery, Amazon sends a series of notifications to let you know that the package is on its way. At any point, you can choose to change delivery locations or “block access” to the car in the Key app, if for some reason you need to run a quick errand or your car won’t be immediately accessible to the delivery person. Amazon will then default to your backup delivery location if access to the vehicle is blocked.

To find your car, Amazon’s couriers will have access to its GPS location and license plate number, as well as an image of the car. An Amazon delivery employee named Christine demonstrated to The Verge how she would use her own device to verify she had found the car (a red Chevy Equinox), scan the package, and then request the vehicle to be unlocked from Chevy’s connected car services. Amazon says it never has access to the customer’s connected car login details and that all communications between the company and the connected car systems are encrypted.

“We only actually do the unlock if its the right person, right place, right car, right time.”

“Note that she doesn’t have a special key or direct access to the car,” Larsen explained during the demo. “It’s going up to the Amazon Key cloud, and it’s going over to the Chevrolet cloud, in this case, which is where the unlock command is issued. We only actually do the unlock if its the right person, right place, right car, right time. Got to pass all those checks.”

Having verified the right car, Christine swiped to unlock it and the Chevy’s trunk opened automatically, revealing a suspiciously neat interior. She dropped in the package, verified its delivery, closed the trunk, and checked to make sure it was locked. “She can’t move on to her next delivery, she can’t see the address, until that happens,” Larsen added.

There is some concern about the vehicle’s connectivity “uptime,” and difficulty Amazon couriers may have accessing the automaker cloud services in low-connectivity areas. Also, Amazon will face a significant challenge in totally reshaping its last-mile supply chain, especially considering they now have to deliver to a location that can shift and change depending on where the car is parked. During the beta testing, Amazon didn’t know the location of the car until up to six hours before the delivery was scheduled to take place, the source with knowledge of the deal said.

Amazon will face a significant challenge in totally reshaping its last-mile supply chain

Automakers have been experimenting with in-car deliveries, operating under the assumption that a person’s car doubles as a storage locker on wheels. In 2016, Volvo launched an in-car delivery option for residents of Stockholm, working with Swedish startup Urb-it. Volkswagen says its ID concept car will also function as a de facto mailbox. Amazon has previously experimented with in-car deliveries, launching a short-lived pilot in Germany with Audi in 2015.

The decision to go with GM and Volvo as launch partners is a reflection of both automakers’ focus on connected car technology. OnStar, a subsidiary of GM, is seen as a leader in subscription-based hands-free calling, navigation, and emergency services. A spokesperson for GM that over 7 million Chevy, Buick, Cadillac, and GMC vehicles will be eligible for this new service from Amazon. Volvo On Call is a similar service that provides subscribers with roadside assistance, remote climate control, and the ability to lock and unlock your car from wherever you are. These high-tech functions made for a natural fit with Amazon, Larsen said.

Still, some people will automatically be turned off by this service, especially after reading that security researchers discovered that Amazon’s cloud-connected camera for in-home deliveries can be disabled and frozen from a program run from any computer within Wi-Fi range. While Amazon’s cloud-connected camera provided a layer of security for those who would want to monitor their in-home deliveries through Amazon Key, the in-car deliveries offer no similar video feed. Amazon says that multiple notifications, plus the option to block access at any time, ensures the customer remains in control of the process.

“It’s safe and secure,” Larsen said. “The only difference is there’s no video here.”

If anything, potential customers may find the in-car deliveries more attractive from a cost perspective. To sign up, you aren’t required to spend $250 on a smart lock and camera like with in-home deliveries, and there’s no installation required. All you need is the right car and the willingness to let Amazon’s delivery employees unlock your vehicle. If you aren’t embarrassed by the empty cans of Red Bull and mountain of unpaid parking tickets, Amazon’s couriers won’t be either.