The Emergency Alert System has been used in the United States since the late 1990s to warn the public during emergencies, and its distinctive attention tone is instantly recognised from television and radio broadcasts. Online, short clips of that tone have been repurposed as memes, often played repeatedly to parody official warnings and give ordinary announcements a sense of false urgency. The humour comes from that mismatch, and because the sound is so familiar, even a fraction of a second is enough to set up a joke in a short video.