Door banging has long been used in film, radio drama and theatre as a shorthand for urgency, authority or trouble arriving without warning, because the sound is instantly recognisable even without a picture. Online, short recordings of knocking have become a staple soundboard effect, shared in prank videos, reaction clips and horror edits where a sudden intrusion needs to land in seconds. Its continued popularity comes from that simplicity: listeners do not need context to understand that someone wants in, right now, and that something is about to happen.