Radio frequency identification (RFID) is a *relatively short-range* (from **less than a foot** of some **passive** tags to about **100 meters for active** tags) wireless technology that uses a tag and a receiver to exchange information. RFID may be deployed using *active tags*, which *have their own power source* and always send signals to be read by a reader; *semi-active tags*, which *have a battery* to power their circuits *but are activated by the reader*; or *passive tags*, which are *entirely powered by the reader*. RFID tags also use one of three frequency ranges. **Low-frequency RFIDs** are used for short-range, low-power tags and are commonly used for entry access and identification purposes, where they are scanned by a nearby reader. *Low-frequency RFID is not consistent around the world*, meaning that tags may not meet frequency or power requirements in other countries. **High-frequency RFID** tags have a longer *readable range at up to a meter* under normal circumstances and can communicate more quickly. In fact, high-frequency RFID is used for near-field communication, and many tags support read-only, write-only, and rewritable tags. The final frequency range is **ultra-high-frequency RFID**, the *fastest to read and with the longest range*. This means that ultra-high-frequency RFID tags are used in circumstances where readers need to be farther away. High-frequency tags have found broad *implementation for inventory and antitheft purposes* as well as a multitude of other uses where a tag that can be remotely queried from meters away can be useful.