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Better clear the junk out of your trunk: Amazon is now offering delivery service to your car.

The online retailer on Tuesday introduced Amazon Key In-Car, a delivery service that drops off packages into people's cars without the need for the owners to be present.

The new delivery option is free for Amazon Prime members and available immediately in 37 cities across the U.S., with more cities rolling out over time.

The service is an extension of Amazon Key, which Amazon introduced last November as a way for delivery people to enter customers' homes using keyless access. The program has received mixed reviews, with some touting it as a solution to package thefts from porches and others seeing it as an invasion of privacy.

With Amazon Key In-Car, customers with compatible vehicles download the Amazon Key App, then link their Amazon account to it. They select the "in-car" delivery option at checkout, and get notifications from the app once their package has been delivered.

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Amazon tried the program out on a select number of customers, who beamed while sharing their experience in an Amazon-produced YouTube video Tuesday morning.

"Woohoo! All my packages are here," said one woman, opening her trunk to reveal three boxes neatly stacked inside. She described herself as a busy stay-at-home mom who frequently gets packages from Amazon and said this enabled her to receive them without worrying about her kids getting woken up from their naps.

Another customer said it helped him keep personal and business orders separate by giving him another delivery site.

But not everyone welcomed the idea.

"Oh god, no," read the top comment on Amazon's YouTube video Tuesday morning. The next comment simply said: "Wtf."

The cars must be parked in a publicly accessible location in order to receive packages, which will be placed either in the trunk or inside the car itself.

Some customers were skeptical.

"Amazon can't find my 3-story building and type in a key code. How do they expect to find and unlock the trunk of my car?" tweeted one person.

The service is available for compatible vehicles from Chevrolet, Buick, GMC or Cadillac with an active OnStar account no older than 2015, as well as customers with a 2015 or newer Volvo vehicle with an active Volvo On Call account, according to Amazon. More models and makes will be added over time.

Amazon can't find my 3-story building and type in a key code. How do they expect to find and unlock the trunk of my car? #AmazonKeyInCar https://t.co/6L0PTBkB0h — NerdyParker (@NerdyParker) April 24, 2018

It isn't Amazon's first alternative delivery site. The company also ships to Amazon Lockers, which are private kiosks at more than 2,000 locations across the U.S.

Amazon said the response to Amazon Key features for homes, like the keyless guest access and customers being able to monitor front doors remotely, prompted them to add in-car delivery.

"In-car delivery gives customers that same peace of mind and allows them to take the Amazon experience with them," Peter Larsen, Amazon’s vice president of delivery technology, said in a statement.