SEATTLE — The first clue that there’s something unusual about Amazon’s store of the future hits you right at the front door. It feels as if you are entering a subway station. A row of gates guard the entrance to the store, known as Amazon Go, allowing in only people with the store’s smartphone app.

Inside is an 1,800-square foot mini-market packed with shelves of food that you can find in a lot of other convenience stores — soda, potato chips, ketchup. It also has some food usually found at Whole Foods, the supermarket chain that Amazon owns.

But the technology that is also inside, mostly tucked away out of sight, enables a shopping experience like no other. There are no cashiers or registers anywhere. Shoppers leave the store through those same gates, without pausing to pull out a credit card. Their Amazon account automatically gets charged for what they take out the door.