NHL arenas normally employ two horns—a high-pitched horn (or a siren, as in the home arenas of the Boston Bruins and Montreal Canadiens) that announces the end of the period (or the start of instant replay reviews), and a much louder, lower-pitched horn 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.