A simple device for signalling the arrival of a deep cast on bottom has been developed and is now in routine use. The device is used either in line with corers or is suspended below as a pilot. When contact of either the ball-breaker or other apparatus is made with the bottom, a small glass sphere in the former is imploded and the resultant signal at the surface is amplified and reproduced over a loud speaker system. The device has been used successfully at depths to 2,700 fathoms.