Abstract: Disclosed is a method and apparatus for indicating the downhole arrival of a well tool. The disclosed embodiment includes placing a magnet on the top releasing plug of a subsea releasing plug apparatus for cementing offshore oil wells, and sensing the arrival of the magnet with a magnetic switch in the well bore at the seafloor. An acoustic signal is sent from the seafloor to the ocean surface over a pipe string in the well at one frequency before the closure of the magnetic switch, and at a second frequency after the arrival of the top releasing plug closes the magnetic switch. The apparatus includes means at the surface for displaying the acoustic signal being received over the pipe string.