Many Bluetooth LE devices (including iOS 7) do something similar -- otherwise you'd be able to track people by all of their BT LE devices which are constantly a

Many Bluetooth LE devices (including iOS 7) do something similar -- otherwise you'd be able to track people by all of their BT LE devices which are constantly advertising their existence. They cycle their advertised MAC addresses every 15 minutes or so (and some provide a "random resolvable address" which you can use to find out the physical BT MAC address after pairing for easier reconnection). From my office in downtown Los Altos, I can currently see a FitBit Flex, a FitBit One and a couple of phones -- the randomized MAC address is all that prevents someone bad from tracking them (BTLE scanners/phones are cheap!). I guess you could still use the 15 minute MAC to track people through a train station or other semi-public space (to gather metrics on where people are coming from and going to). If you had a lot of antennas then you could circumvent the MAC cycling by linking devices in the same area with the same name and similar RSSI...