This tone comes from Facebook Messenger, the messaging app built around Facebook, where it serves as the default sound for incoming voice and video calls. Because millions of people hear it on their phones every day, it quickly became shorthand online for someone calling at an inconvenient time. Creators on TikTok, YouTube and Instagram began dropping the short clip into comedy skits, reaction videos and pranks to trigger that instant recognition. It remains popular because it needs no explanation: almost anyone who uses messaging apps knows immediately that a call is coming in.