Going into a store without anyone working on a cash register - and that being the norm? It's getting another step closer to reality, as Amazon is announcing an expansion of its cashier-less stores.

The company is planning stores in Chicago and San Francisco to go along with the one it launched in Seattle this year. While it is confirming the new stores are coming, Amazon isn't saying when. Here's how they work: shoppers enter the stores by scanning a smartphone app.

Once inside, they can take items and walk out. Amazon's technology, including overhead cameras, keeps track of what they buy and charges customers once they leave.