Radio signals are transmitted via electromagnetic fields tuned to radio frequencies from tags attached to objects to automatically identify and track them. Some tags are powered by the electromagnetic field emitted by the recognizer, without the need for batteries; Some tags have their own power source and can actively emit radio waves (electromagnetic fields tuned to radio frequencies). Tags contain electronically stored information that can be identified within a few meters. Unlike bar codes, rfid tags do not need to be in the recognizer's line of sight and can be embedded in the object being tracked.

Rfid technology is used in many industries. By attaching the tag to a car in production, the factory can track its progress on the production line. The warehouse can track where the drugs are. Rfid tags can also be attached to livestock and pets to facilitate positive identification of livestock and pets (positive identification means preventing multiple animals from using the same identity). Rfid id cards allow employees to enter locked parts of buildings, and RFID transponders in cars can be used to collect toll lanes and parking lots.