RFID tags can be active, passive or battery-operated passive. An active tag includes an on-board battery and it transmits its ID signal periodically. A battery-controlled passive (BAP) involves a little battery on board. It is activated in the presence of a RFID reader. A passive tag is smaller and cheaper as it does not have battery. Instead, radio energy transmitted by the reader is used by the tag.
To activate a passive tag, it is enlightened with a power level roughly a thousand times stronger compared to signal transmission. If you want to know more about RFID, it is suggested to search for RFID Chip Timing Bloomington Indiana on the Internet.