NEW YORK (AP) — Amazon, which opened a cashier-less store in Seattle this year, plans more locations in Chicago and San Francisco.

The company confirmed Monday that Amazon Go stores would open in the two cities, but didn't say when. The store openings were first reported by the San Francisco Chronicle and The Seattle Times .

Shoppers enter the stores by scanning a smartphone app. Once inside, they can take soda, salads or anything else off its shelves and just walk out. Amazon's technology, including overhead cameras, keeps track of what they buy and charges customers after they leave.

Opening more stores is yet another sign that Amazon is serious about expanding its physical presence. It bought grocer Whole Foods last year, which gave it 470 stores, and has opened more than a dozen bookstores.