iBeacon. They know what shelf you're standing in front of. What products you touch and read.
Ever been in an Apple store? Look up. In the dark voids between the edge-to-edge backlit ceiling. There are secrets there. Watching you.
Macys pioneered it before there even were Apple Stores. Back when most people didn't even know their phones had Bluetooth.
Not what iBeacon does but an entertainingly dramatic description nonetheless.