A horn fashioned from the tip of an orca rib, studded with ruby and adorned with leafed copper.
When blown in the water, will produce a booming sound that can be heard for 20 leagues in any direction. This sound will echo off of any wooden vessel (floating or sunk), alerting the creature who blew the horn to the ship’s existence, direction, and distance.
Beware sharks and Sahuagin that may answer the horn’s call.