Abstract: An improved transponder for transmitting an identification of an animal or the like is described which is sufficiently miniaturized to be syringe-implantable, thus avoiding the necessity of surgical procedures. The transponder comprises a coil which receives an interrogation signal and transmits an identification signal in response thereto. The transponder receives the energy required for transmission by inductive coupling to an interrogator. A single integrated circuit chip is provided which detects the interrogation signal, rectifies it to generate power needed for transmission, stores an identification of the transponder and hence of the animal in which it is implanted, and generates a frequency-shift-keyed, Manchester encoded identification signal in response to the interrogation signal. The device transmits the identification signal in real time, that is, immediately upon commencement of the interrogation signal, such that no discrete elements for energy storage are required.