Abstract: An apparatus for non-intrusively indicating the passage of a pipeline pig having a housing adapted to be supported adjacent the exterior surface of a pipeline through which a magnet carrying pig moves, the housing containing an armature formed of pole pieces of paramagnetic material having a narrow gap therein that receives a solid-state magnetic sensing member, the sensing member providing changing electrical characteristics in response to changes in ambient magnetic field intensities, and an indicator pivotally attached to the housing and normally held in a ready position by a latch, the latch being operated by a circuit controlled by the magnetic sensing member so that the flag is released to move to an operative position in response to a changed magnetic field intensity caused by the passage of a magnet carrying pig, the armature within the housing serving to increase the sensitivity of the magnetic sensing member.