Most modern smartphones have an RFID chip inside them. The process could be as simple as first taking RFID readers into Antifa gatherings to compose a list of devices present and then seeing if any of those specific devices pinged at those gatherings get pinged again by RFID readers surreptitiously placed near FBI building entrances which have restricted entry.

Most modern smartphones have an RFID chip inside them which can be pinged by any RFID reader. The process could be as simple as first taking RFID readers into Antifa gatherings to compose a list of devices present and then seeing if any of those specific devices pinged at those gatherings get pinged again by RFID readers surreptitiously placed near FBI building entrances which have restricted entry.