RFID is a technology used for tracking assets and personnel that have an electronic tag attached to them. A RFID system consists of four items: an interrogator or reader, an antenna attached to the reader, the tag or transponder attached to the asset, and the software required to control the reader. The interrogator reads what is in the tag's memory and can send new information to the tag. The antenna attached to the reader determines where the tag can be read. The type of system determines the kind of antenna that will be used. A tag is essentially an electronic chip with an antenna attached to it that allows the chip to communicate with the reader. An active tag has a battery that allows it to transmit to the reader on its own. A passive tag has no battery and is powered only by the radio frequency energy received from the reader's antenna. A semi-passive tag has a battery assist that only powers chip circuitry on the tag. The type of asset to be tagged and the frequency requirements will determine the tag best suited for system performance. Inmate and officer tracking systems have recently been used at a few locations in the United States. These systems use tamper-proof active tags with the ability to locate and track a person within the reader antenna range area. The movements of the person tagged can be recorded and tracked in real time. RFID systems can also be used to track vehicles, keys, and other corrections assets, including medical records and supplies.