The active transponder includes an input amplifier (26) arranged between an envelope detector (8) and a demodulation circuit (28). It further includes an activation unit (30) for the input amplifier and also for the demodulation circuit, which is formed by a frequency changer or mixer circuit (32), which decreases a significant modulation frequency of the modulated signal received by the antenna to a low frequency, the resulting low frequency signal then being amplified and filtered by low frequency elements. The activation unit thus consumes little electric power and sends a wake up signal to the elements operating at a high frequency when it detects said significant modulation frequency, in a very selective manner.