The Thunder Ear is a device made by Hiccup. It was made to locate the Screaming Death through its scream. Stoick also saw it as a way to hear enemy ships, gossip when he heard Gobber saying how useless Stoick would be without him, as well as cries of three baby Thunderdrums. Later, those same baby Thunderdrums destroyed the Thunder Ear.
The Thunder Ear is a large, silver and red trumpet-like instrument. A sentry can place his or her ear close to the small end, and they will hear anything that the large end was pointed at.
Hiccup was getting ready to test the Thunder Ear, with the help of Toothless, Fishlegs, and Meatlug when Stoick and Thornado were making their rounds around the island. Stoick later helped with the test when he listened from it to hear Fishlegs and Meatlug sing from afar, the Chief had thought that it was a joke until his son handed him a spyglass, so he would see the singing Viking and Gronckle. After seeing how useful that the ear could be, Hiccup told his father that it could help them find the Screaming Death by listening out for it through it's screaming roar, just as Stoick saw it as a way to hear their enemies coming; as well as hearing gossip about him when Stoick heard Gobber calling himself his "right hook man".
The ear also picked up the sound of three baby dragons, since the two didn't know what type of dragon they were hearing, they set out to find them. Once there, they discovered three young Thunderdrums, Bing, Bam and Boom. When the two Vikings got back and when Gobber found out how the Chief heard him, he came up with a different name for Thunder Ear; that might have something to do with "eavesdropping".
The ear was later destroyed by Bam as he sonic blasted inside of it, breaking it apart and then blasted the pieces away.
However, it was later revealed in "Gruff Around the Edges" that the Thunder Ear has been repaired or rebuilt and placed on Dragon's Edge. It is likely now used in an attempt to locate the Dragon Hunters before they attack the Edge. Ruffnut and Tuffnut are also known to use the Thunder Ear in reverse as a means of doing their morning show, speaking through it instead of listening through it.
- It is possible that the Thunder Ear is the prototype for the horn that is blown to signal the arrival of the black sheep in Dragon Racing.
- The exact model of the Thunder Ear (although much smaller) appears in the DreamWorks Trollhunters episode "Grand Theft Otto".