Patent US 7,586,397

Interactive radio frequency tags that are responsive to external stimuli to change state are disclosed. The tags preferably include a passive radio frequency transponder, having an antenna, an interface for receiving an external stimulus, and one or more integrated circuits responsive to the external stimulus received at the interface to change the state of the transponder. Also disclosed is a “sensor tag” which changes state in response to a particular environmental stimulus. In addition, either of these “button” or “sensor” features may be combined with an output feature which visually, audibly, tactilely or otherwise signals the state or change of state of an RF tag, or the tag may be designed to produce an output in response to the external stimulus of the RF signal received at the tag's antenna.