About RFID

Passive RFID tags (most common): no battery, require an external power source

Active RFID tags: contain a battery, can transmit signals autonomously and can transmit over longer distances

RFID tags are used for: - passports - race timing - transportation payments - product tracking - transportation and logistics - animal identification - inventory systems - human implants - libraries

Potential risks
RFID for authenticating people is very risky due to the way you can read RFID tag. It is possible to read content of RFID tag just by passing by the person who has it implanted.