Abstract: A pig passage indicator is provided by the present disclosure and includes an elongate cylindrical hollow body having a sleeve which threads only inside the body. The sleeve captures a moveable pin or rod and a compressed resilient coil spring. The coil spring and pin connect with a plunger which has a contoured or hemispherical tip. The tip is positioned so that it protrudes into the pipeline. When a pig passes, it nudges the tip of the plunger, moves the plunger against the coil spring, and operates the rod to thereby form an alarm signal. The interior of the body is isolated by first and second spaced seal rings to define a fluid isolated chamber. Pipeline fluid does not get into this chamber.