Trident of warning
From Ardrana
The trident of warning enables its wielder to determine the location, depth, species, and number of hostile or hungry marine predators within 240 feet. It must be grasped and pointed in order for the person using it to gain such information, and it requires one round to scan a hemisphere with a radius of 240 feet.
Note: This item originally appeared in this form in the 2nd Edition Dungeon Master Guide for the Advanced Dungeons & Dragons game by TSR. Its inclusion here is for the purposes of providing context for the campaign only.