A method and system for detecting information relating to the location of a radio IC tag, using an interrogator unit. In one implementation of such method and system, a radio IC tag is securely attached to a fixed object, and a mobile object that has an interrogator unit moves into communication range with the radio IC tag. As the interrogator unit sends radio waves to the radio IC tag, the radio IC tag existing in the communication range sends reflected waves to the interrogator unit. When the interrogator unit receives the reflected waves, it detects and demodulates the reflected waves. The interrogator unit then reads information relating to the location of the radio IC tag as the information stored in the radio IC tag.