DALLAS (CBSDFW.COM/CNN Money) – Amazon has turned the trunk of your car into a mailbox. The tech giant has just launched a service in 37 American cities that delivers packages to the trunks of cars for free. But you must be a Prime member to qualify for trunk delivery.

You also need to have an eligible vehicle for the service to work. Almost every Chevrolet, Buick, GMC, Cadillac and Volvo with a model year of 2015 or newer are compatible. GM owners must have an active OnStar account. Volvo owners need an active On Call account. These systems provide remote access to vehicles, which makes Amazon Key In-Car possible.

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In November, the company launched Amazon Key, which uses a camera and smart lock so that Prime members can have their deliveries brought into the home. The same app is required for Amazon Key In-Car. The service relies on the vehicle’s internet connection to remotely open the trunk so that packages can be delivered.

Amazon delivery people receive one-time access to the trunk. An alert is sent to customers when the process is complete.

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During checkout, a new options appears for “in-car delivery,” and customers are then given a four-hour delivery window. The car must be parked within a couple blocks of the delivery address, in a publicly accessible spot. The customer adds their car’s color, make and model using the app, and the delivery person finds the vehicle with the aid of GPS.

There are some restrictions on what can be delivered to a car trunk. Items cannot be valued at more than $1,300, weigh more than 50 pounds, exceed 26 x 21 x 16 inches, or be fulfilled by a third-party seller.

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For now, the service is only available in 37 cities including Dallas, Los Angeles and Chicago. More locations are coming soon.

For urban residents, this could be a game changer. So-called ‘porch pirates,’ the people who walk off with delivered packages that are left outside of homes, have been a problem for many residents. Facebook users regularly post videos of their packages being stolen. Doorbell cameras do not seem to deter theft.

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