The "Vuvuzela" - a Stadium horn.
The Vuvuzela is a plastic horn about 2 ft long that produces a single note, usually around Bb3 .
The articles provided here are:
Vuvuzela - WIKIPEDIA - an article describing the instrument
(Note the section on "Health Concerns" relating to the Noise Levels).
Fun Facts - 10 Things to Know about the Vuvuzela