The door chime is a standard safety warning in Ford cars and trucks, designed to alert the driver when a door is open while the key is in the ignition or the headlights are still on. Because so many people recognize the sound from daily driving, clips of it began circulating on soundboards and in short videos as a shorthand for forgetfulness, carelessness and stubborn inattention. It remains popular because the tone is instantly familiar, easy to loop, and immediately tells viewers that something obvious has been overlooked.