When the battery is used to power a sensor, they are often called sensor tags. They typically are smaller and cheaper than active tags, but have greater functionality than passive tags because more power is available for other purposes. This onboard power is used to operate the circuitry on the chip, storing information such as ambient temperature.
Semi-passive tags can be combined, for example, with sensors to create smart dust — tiny wireless sensors that can monitor environmental factors. A grocery chain might use smart dust to track energy use, or a vineyard to measure incremental weather changes that could critically affect grapes.
Some literature uses the terms "semi-passive" and "semi-active" interchangeably.
- Guidelines for Securing Radio Frequency Identification (RFID) Systems, Glossary, at B-3.