If so, what are they?
The main power source for active RFID systems is a battery. Different tags have different batteries, depending on the tag size and battery life required. Some active tags use solar energy, but these are not common. It is possible to generate energy from vibrations, but to my knowledge, there are no commercially available active tags that currently do so.
—Mark Roberti, Founder and Editor, RFID Journal
How Can I Ensure Tag Security? »