<Li> in ice hockey (especially in the NHL) </Li> <Li> in the NLL </Li> <Li> Major League Baseball </Li> <P> NHL arenas normally employ two horns--a high pitch horn that announces the end of the period (which is also used to indicate the start of instant replay reviews), and a much louder, lower pitch horn that is sounded when the home team scores and / or wins a game . Some MLB stadiums use horns for similar purposes, such as when a member of the home team hits a home run . In many places, air horns are used for signaling the end of the period or quarter on scoreboard systems . </P>

Where did the mlg air horn come from