Abstract: The present invention includes a ferrous conduit mounted over an aperture in the pipeline, launch tube, or receiver through which the pigs pass. A non-magnetic sensing rod is reciprocally mounted within the conduit with the rod extending through the aperture and into the pipeline. That end of the non-magnetic sensing rod extending into the pipeline has attached thereto a head with a lower rounded surface for engaging the pigs. A non-magnetic end cap is secured to the upper end of the conduit and a non-magnetic magnet holder with a magnet disposed therein are mounted on the upper end of the rod. A magnetically operated switch is mounted adjacent the non-magnetic cap. The conduit shields the magnetic field of the magnet from the switch until a pig is detected. Upon the engagement of the head with a pig, the magnet on the upper end of the sensing rod moves above the conduit inside the non-magnetic cap and sends a magnetic flux to the magnetically operated switch.