The Storm Ear has a tuning fork, which is attuned to a particular sound frequency. For the purposes of the game, the tuning fork in the Storm Ear is set to the same frequency as the cries of the upset baby Luminous Krayfin. When the sound waves from the Krayfin's cries reach the Storm Ear, the tuning fork starts vibrating, thus allowing the player to follow the baby.
The Storm Ear appears in the Expansion, "Secret of the Leviathan". When Lumie, a baby Luminous Krayfin disappears, Hiccup creates the Storm Ear, in order to find it. He hands it to the player, who uses it to follow the dragon on Impossible Island. There, the player uses it again to find the baby Krayfin.