RFID tags need a power source to perform functions such as sending radio signals to an RFID reader, storing and retrieving data, and performing other computations (e.g., those needed for security mechanisms). RFID tags can obtain this power from a battery or from electromagnetic waves emitted by readers that induce an electric current in the RFID tags. The power requirements of a RFID tag depend on several factors, including the operating distance between the RFID tag and the reader, the radio frequency being used, and the functionality of the RFID tag. In general, the more complex the functions the RFID tag supports, the greater its power requirements. For example, RFID tags that support cryptography or authentication require more energy than RFID tags that are limited to transmitting an identifier.