After more than a year of testing, Amazon.com Inc will open its checkout-free grocery store to the public on Monday, proceeding with a business experiment that could could dramatically alter brick-and-mortar retail operations.

Amazon Go, which will debut in Seattle, utilizes cameras and sensors to track what shoppers remove from the shelves, and what they replace, then bills customers after they leave the store using credit cards on file. Establishing such a setup eliminates the need for checkout services and headaches.

Grocers view the opening of Amazon Go as another potential disruption by the world’s largest online retailer, which, in 2017 purchased high-end supermarket chain Whole Foods for $13.7 billion. Since shoppers are deterred by long checkout lines, a company that offers a no-wait grocery shopping option has a distinct advantage in the marketplace.

Amazon said that the company does not intend to add the checkout-free technology in Whole Foods stores, and did not indicate whether it will add more Amazon Go locations to its portfolio.

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The convenience-style store opened to Amazon employees on Dec. 5, 2016 in a test phase. At the time, Amazon said it expected members of the public could begin using the store in early 2017.

But there have been challenges, according to a person familiar with the matter. These included correctly identifying shoppers with similar body types, the person said. When children were brought into the store during the trial, they caused havoc by moving items to incorrect places, the person added.

Gianna Puerini, vice president of Amazon Go, said in an interview that the store worked very well throughout the test phase, thanks to four years of prior legwork.

“This technology didn’t exist,” Puerini said, walking through the Seattle store. “It was really advancing the state of the art of computer vision and machine learning.”

“If you look at these products, you can see they’re super similar,” she said of two near-identical Starbucks drinks next to each other on a shelf. One had light cream and the other had regular, and Amazon’s technology learned to tell them apart.

The 1800-square-foot store is located in an Amazon office building. To start shopping, customers must scan an Amazon Go smartphone app and pass through a gated turnstile.

Ready-to-eat lunch items greet shoppers when they enter. Deeper into the store, shoppers can find a small selection of grocery items, including meats and meal kits. An Amazon employee checks IDs in the store’s wine and beer section.

Sleek black cameras monitoring from above and weight sensors in the shelves help Amazon determine exactly what people take.

If someone passes back through the gates with an item, his or her associated account is charged. If a shopper puts an item back on the shelf, Amazon removes it from his or her virtual cart.

Much of the store will feel familiar to shoppers, aside from the check-out process. Amazon, famous for dynamic pricing online, has printed price tags just as traditional brick-and-mortar stores do.