And when the door opens to let you in, if someone else follows you in, who does not have an Amazon account, and he grabs a bunch of stuff and leaves, what happens?
There will be shoplifting problems at stores such as this. I hope they have thought through how to deal with it. Otherwise this experiment, which should work well as long as all are honest, will fail badly.
I believe it is done with facial recognition cameras. There were dozens of cameras on the high ceilings. And most likely camera lenses in front of items on the shelves. You don’t scan any items with your phone at all. You go through a turnstile that only turns if you scanned your Amazon ID. I believe your photo is taken at a dozen angles at that moment.