The siren comes from Call of Duty: Modern Warfare 2, released in 2009, where earning a tactical nuke required 25 kills without dying and ended the match with a huge explosion. The warning alarm played for all players in those final seconds, making it one of the most recognisable sounds from that era of multiplayer shooters. As gameplay clips spread on YouTube and later TikTok, editors reused the siren outside matches to signal an unstoppable moment, a big reveal, or a joke about to land, keeping it popular long after the original game.