A wireless recording device can be interrogated to determine its identity
and its state. The state indicates whether a particular physical or
chemical event has taken place. In effect, the physical or chemical event
is recorded by the device. The identity of the device allows it to be
distinguished from a number of similar devices. Thus the sensor device may
be used in an array of devices that can be probed by a wireless
interrogation unit. The device tells the interrogator who it is and what
state it is in. The interrogator can thus easily identify particular items
in an array that have reached a particular condition.
