DSMB’s, or Delayed Surface Marker Buoys, are a diver’s best friend. Used for communication with surface crews or boats while the diver is still at depth.
They can be used to signal the need for a boat pick up, as a distress signal, a marker of a location (maybe of that sunken treasure you found?), or to indicate the need for additional air on long decompression stops.
Kg. Genting, Tioman Island, Malaysia. 