Abstract: The proposed device is an identification system having an interrogator/receiver and a passive transponder. The interrogator/receiver includes a clock signal generator (1) a group of bandpass filters (5), a section to decode the data received, and an interrogator coil (4) for inductively coupling the interrogator/receiver to the transponder. The transponder includes a section (E) for picking up the power signal transmitted by the interrogator/receiver, a section (F) to codify the signal obtained according to a predetermined code stored in a memory (15), and a section (G) for phase modulating the codified data so as to allow air transmission. Particularly, the bandpass filters (5) are capable of detecting a frequency band width lower than one thousandth of the signal's frequency.