The ka-ching comes from mechanical cash registers first popularised in the late 1800s, when a bell rang each time the drawer opened to stop theft and signal a sale. That bell and drawer combination became the universal audio shorthand for commerce in cartoons, films and television for decades. As registers went electronic, the recorded effect survived online as a stock sound for memes and edits. Creators still reach for it because one ring instantly means money earned, spent or saved, with no explanation needed.