Amazon Go, the Amazon cashier-less convenience store, is coming to San Francisco and Chicago -The first location opened in Seattle in January after a year of testing.

To shop in the Seattle store, which is about the size of a 7-Eleven, customers must first download the Amazon Go app and link it to a payment method. Then they open the app on their phone and scan it at one of the four turnstiles to enter the 1,800 square foot store. Once inside, cameras in the ceiling, sensors on the shelves and a massive amount of computing power track every item they pick up and what goes into their pockets or bags. To check out, you just walk out — it's called Just Walk Out technology.

The actual Amazon Go store is extremely tech-heavy, was expensive to build and can only sell a narrow range of specially-selected items — nowhere near the 50,000 or so items a typical supermarket stocks. But with time that could change, making the possibility of a true revolution in the way we interact with brick and mortar stores.