Radio frequency identification transponder is a device that uses radio waves to communicate with a computer system. Typical uses of RFID transponders include timing of sporting events, inventory control, and the collection of tolls on highways.
There are two types of RFID transponders: passive and active. An active transponder has an internal battery, similar to the battery contained in a wristwatch. When the battery is exhausted, the transponder is no longer usable. A passive transponder has no internal battery. Instead, the sensor broadcasts radio waves to the transponder, and the transponder converts the radio energy into electricity. The electricity is collected in a capacitor until sufficient voltage is stored to power the microprocessor on the transponder. Passive transponders have an indefinite lifespan.