A wearable RFID device is provided for use in an event-based interrogation zone. The zone contains terminals with RFID readers. The device has an element worn by a user and an attached or embedded RFID tag. The tag has stored data representing a UniqueID of the tag, and a stored funds balance. The tag is programmed to activate an otherwise inactive one of said terminals upon presentation of the tag to the RFID reader of said terminal in a first tap, and communicate its UniqueID to the terminal for validation. Upon validation and following a second tap of the tag at the RFID reader, the tag's stored funds balance can be changed by the amount of a transaction run through said terminal. A temporary installation of a system of RFID-based terminals and user-worn RFID devices is also provided for use within an event interrogation zone.