Comment by jlarocco

I was researching bluetooth low energy for a project, and discovered "Beacons": https://en.wikipedia.org/wiki/Bluetooth_Low_Energy_beacon

What's more insidious than just tracking people through the store is that the beacons can collect the bluetooth IDs of the devices they've seen and send it off to advertisers, who can use the UUID to connect a person's offline shopping with the online advertising profile they've built up for the person.