This is what NFC Pay is for. Strip away all the bullshit about tapping and paying bills. Underneath it all is an RFID tag on the phone. Anyone who can put up a transmitter within 10 meters of a road or any place where people pass by, can remotely trigger the NFC RFID and get the serial number. NO SECURITY AT ALL.
Since that RFID is on a phone that belongs to you and that you use for all kinds of login and authentication tasks, simply cross referencing the RFID serial number with your identity makes it possible to track you wherever you go.
This is what RFID was invented for back in the late 1950's. In the early 60s they did lots of experiments with people by putting RFID tags up people's sinuses and tracting them. Back then they had a whisker antenna sticking out. They used the UFO scare as cover for their experiments on unsuspecting civilians.