What about beacons being not so one-way? Assuming you enabled the beacon on your own phone for whatever reason (some fancy app), then information can be gathered easily without you giving permission or noticing at all.
WiFi is active and yes, wiretapping is possible, at least for locating you. Hardware/software for doing this though is not readily available as far as I can tell.
Finally, iBeacons: very simple software running on a passive BLE device that simply records all BLE UUIDs passing by, that's all!