A storage device has a separate type magnetic head and a discrete type magnetic recording medium on which recording tracks and recording disabled areas are alternately formed. At least one inductive sensor is positioned near the internal surface of the electrically insulating structure so that the inductive sensor delivers a signal when a lightning arrester strip is passed through by a lightning current I. In the case of a deflector for a line of hydrophones towed by a ship to carry out seismic tests at sea, the noise disturbing the hydrophones is reduced.