Compass

The compass is an item found in dungeons that lets you see the hidden treasure chests in a dungeon on your Dungeon Map. It also indicates the where the boss is located.

In A Link to the Past and Link's Awakening the compass does not show the locations of hidden chests.

An additional feature is the tone alert upon entering a room with a hidden key. This feature was first introduced in Link's Awakening. It has been present in all Gameboy title Zelda games since.