I don't know whether Android has adopted the same protocol, but on iOS, that's https://en.wikipedia.org/wiki/IBeacon: basically an API where apps can register an OS event-handler plugin to run in response to the detection of [basically, but not exactly] specific Bluetooth MACs.
The scary thing is, iBeacon handler don't have to do the cute "hey you're in this store, click to open the app!" sort of thing. They can run completely in the background, just reporting "hey boss, they're in the shoe section of Store #3313 now! Now they're in the produce section! Now they're gone." And, as far as I know, there's no way to turn off the tracking behaviour while keeping the helpful "activation suggestion" behaviour.
The scary thing is, iBeacon handler don't have to do the cute "hey you're in this store, click to open the app!" sort of thing. They can run completely in the background, just reporting "hey boss, they're in the shoe section of Store #3313 now! Now they're in the produce section! Now they're gone." And, as far as I know, there's no way to turn off the tracking behaviour while keeping the helpful "activation suggestion" behaviour.