Ben Fox Rubin/CNET

I visited the Manhattan Classic Car Club along the Hudson River last Friday. But I wasn't there to gawk at the lime green Lamborghini or vintage orange Bronco. I was there to check out a very sensible red Chevy Equinox.

With the help of that Chevy, a team from Amazon put together a demonstration of a new right-to-your-car-trunk delivery service, called Amazon Key In-Car, which it unveiled publicly Tuesday.

In a parking lot outside, a woman in an Amazon delivery uniform pulled a shipping box from a van nearby and walked over to the Chevy. She used an app for Amazon delivery workers on her phone to unlock the car, then placed the box in the trunk and shut the door. She then used the app again to lock the car. Voila.

Now playing: Watch this: Here's how Amazon Key In-Car delivery works

As its name suggests, the new program builds off Amazon Key in-home delivery, which launched in October. The free in-car service is available for Prime members to use starting Tuesday, but it's only rolling out to the 37 US cities where Amazon Key is available and for now only works for newer cars from GM and Volvo.

"The in-home service is working great, and from the very start we knew we wanted to take it beyond the home as well," Peter Larsen, Amazon's vice president of delivery technology, told me Friday.

In-car delivery is another way Amazon is working to ship packages as quickly and seamlessly as possible, in hopes that people will buy more from the e-retailer and not stop at a rival store. The company also places lockers in lobbies of convenience stores and apartment buildings, is testing shipping via drones, and offers free two-hour deliveries for Prime customers through Prime Now.

Key also appears to be growing into a more important part of Amazon's plans, with the company expanding Key's keyless entry feature nationwide this month and weighing adding more hardware to the program. Using Key, Amazon could become a bigger player in people's connected homes, while it also cuts down on stolen or water-damaged packages.

If they're going to order a bunch of chocolate in Arizona in July, they might not choose to have it dropped in the back of their car. Peter Larsen, Amazon

But trying many new concepts has brought problems. When Amazon Key first launched, it received plenty of complaints that it was too intrusive and gave Amazon too much control over people's front doors. That controversy may not resurface with the new in-car service, since the car is a far less private and personal place than the home.

Sucharita Mulpuru, an e-commerce analyst for Forrester, said her company's research shows that most shoppers don't use Amazon's newer shipping concepts like Prime Now, but that's not the point.

"It's for the most part a way for Amazon to position itself as a leader in customer-centricity," she said. "I don't think they are naive thinking most of the things they try are going to be mainstream."

Coming to GM and Volvo cars

Because of its current limitations, Key In-Car may also gain only a small following, at least at first.

The new service requires connected cars that can be unlocked from afar, allowing drivers to open the vehicles using their Amazon apps. So Key In-Car will be available only for customers who have cars from GM-owned Chevrolet, Buick, GMC or Cadillac with active OnStar accounts, or Volvo cars with active Volvo On Call accounts. All vehicles need to be 2015 models or newer.

Amazon said more makes and models will be added over time.

Thanks to those connected car services, customers can park their vehicle anywhere in a roughly two-block radius of their regular delivery address and the driver will find it. In case of any problems, the driver will default to that address for the delivery.

Enlarge Image Ben Fox Rubin/CNET

Amazon did a small, short-term test of in-car deliveries back in 2015 in Germany that required access codes to work. Larsen said Amazon learned from that pilot to create the new, much more expanded program that required no access codes this time around.

The car service will use the same third-party delivery drivers used for Key. One of the few notable differences between the home and car service is that home deliveries require a camera installation, while car deliveries don't.

Larsen said Amazon Key has made deliveries in all 37 cities where the service is available, though he didn't offer specific numbers on how many people have adopted Key.

So far, he said, Key is "working as designed," with fewer redeliveries of packages. Adding services like house cleaners and dog walkers to Key is coming later this year, he added.

Customers will be able to choose from tens of millions of items for in-car delivery. Asked what Amazon won't deliver inside a car, Larsen mentioned the obvious big boxes that won't fit and high-value items that need a signature.

"Customers are smart and they will think through that themselves," he said. "If they're going to order a bunch of chocolate in Arizona in July, they might not choose to have it dropped in the back of their car."

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