Patent ID: 8887799

Claim:
An indicating device for signaling passage of a launched object through a central flow bore of a tool comprising: a. a body member connected to said tool having a first chamber in pressure communication with said central flow bore, a second chamber at substantially atmospheric pressure, and a substantially solid and non-magnetic pressure sealing barrier disposed between said first and second chambers, wherein said barrier isolates said first and second chambers from each other; b. a mechanical trigger pivotally mounted within said first chamber, wherein said mechanical trigger does not extend beyond said barrier, is rotationally displaced when said launched object passes through said central flow bore, and causes a change in magnetic field across said barrier when displaced; c. a sensor wholly disposed within said second chamber, adapted to sense when said magnetic field changes across said barrier resulting from displacement of said mechanical trigger, wherein only said magnetic field is transmitted between said first and second chambers; and d. a signal device that produces a signal when said sensor senses said change in magnetic field across said barrier.