Except that I don't know what that sound means. I know what the one my device makes is, but I've never heard the others. Unless it's a human voice saying, "This conversation is now being recorded" I can't be expected to know what a random beep from a device means. It could just mean the person got a notification or something. (And even if it is a recognizable sentence, it assumes I understand the human language the device is set to.)