Amazon is taking the growing curb-side delivery trend a step further — now shoppers don’t even have to be inside their cars to get their items. The online retailer announced Tuesday it has begun delivering packages to newer cars with OnStar service in 37 cities, including Tampa and St. Petersburg. Deliveries can be placed in customers’ locked cars through the new "Key In-Car" service. Meanwhile, traditional retailers such as Target and Walmart have been expanding their pick-up options to include curb-side deliveries to stay competitive. "People don’t like leaving their cars," said Steven Kirn, a lecturer at the University of Florida’s Warrington College of Business. More than half of fast-food is already sold through drive-thrus, Kirn said. Now the ability to order items from your smartphone has made the already proven concept adaptable for big retailers. "There’s no doubt convenience is a big deal," he said. "The natural evolution is to give people more choices on how they shop." Amazon already gives its customers — and Prime members in particular — a lot of options: Free shipping on many two- to three-day deliveries, Amazon locker pick-up locations, Whole Foods grocery home deliveries, and now packages straight into car trunks. Prime members that have OnStar in their 2015 or newer Chevrolet, Buick, GMC or Cadillac vehicles or those with 2015 or newer Volvo vehicles with an active Volvo On Call account can use the new service. Shoppers will have to download the Amazon Key App, where they can link their connected car to their orders. The deliveries will be placed inside cars parked in accessible areas — such as the home driveway or workplace parking lot — then secured. "Receiving a package securely and reliably in your car, without you having to be there, is something we think many people will appreciate," said Atif Rafiq, chief digital officer at Volvo Cars. "This mix of car and commerce is starting the next wave of innovation and we intend to be at the forefront." Customers can check the app to ensure they’re parked within range of the delivery location the day the package is arriving. The app notifies the users with the expected four-hour delivery window and when the package has been dropped off. Users can also check when their car is unlocked and locked again after the order is complete. For shoppers who aren’t comfortable with leaving items in their cars but still want to shop on the go, Target and Walmart are creating similar platforms. RELATED: Amazon partners with Best Buy on smart TVs "I think it’s an incredible time of transformation where everybody is trying to find the sweet spot in terms of balancing technology and the physical presence and meeting the needs of the consumer," said Scott Shalley, CEO of Florida Retail Federation. About 1,200 Walmart stores already have grocery pick-up, where personal shoppers fill orders and take the bags out to shoppers’ cars so they never have to leave the driver’s seat. RELATED: Tampa Bay area doesn’t make cut as Amazon second headquarter finalist Walmart officials have said they plan to add another 1,000 pick-up locations, as well as expand its grocery delivery to 40 percent of the country by the end of 2018. Tampa Bay shoppers were among the first in the country to have access to both options. In the last two months, Target started putting special "Drive Up" lanes in parking lots across Florida, including at least 10 Tampa Bay locations. While Walmart’s service focuses on perishables and fewer general merchandise options — so, no big-screen TVs — Target’s doesn’t include fresh foods, but most other items from big electronics to baby care items. Target store officials said during the "Drive Up" trial run in chain’s ba of Minneapolis and St. Paul, Minn. online orders went up 10 percent within two weeks. Diapers and paper towels were among their top sellers. MORE: Click here for more business news For those who don’t want to stop at the store at all, Walmart mans its own grocery delivery service; Whole Foods, owned by Amazon, uses the online retailer to manage theirs; and Target and Publix rely on personal shoppers to deliver orders through the app Shipt. Furthermore, Walmart is even testing direct-to-fridge deliveries in the Silicon Valleyby partnering with a home-security company. The Amazon Key service already allows deliverers to put items inside Tampa Bay shoppers’ homes if they so choose. While "Key" kits include an Amazon security camera, no such equipment is needed for the new in-car service. Kirn suspects not all shoppers will be willing to let delivery staffers into their homes or cars, despite the lure of convenience. "How much are you will to disclose and how much access are you willing to give to people that are unnamed," he said, "to your car, house, whatever? Some people are going to have qualms about it." Kirn said that means retailers have to offer all available options, including brick-and-mortar stores, to attract all types of shoppers. "It’s the same thing we were starting to deal with over 10 years ago," he said. "Shoppers want to shop anywhere at anytime through any medium." Information from the Associated Press was used in this story. Contact Sara DiNatale at [email protected] or (727) 893-8862. Follow @sara_dinatale.