The integrated circuit contactless reader has an antenna coil (L1) magnetically coupling to the integrated circuit (5). A magnetic field transmitter (MP) transmits pulses of short duration. A diode (D1) and filter (F1) extract the pulse envelope (SE) from the coil. A pulse surveillance detector (DETC) detects the pulse amplitudes, detecting an envelope pulse amplitude variation when the integrated circuit is in the vicinity of the reader.
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