RWR stands for radar warning receiver, a cockpit system fitted to military aircraft such as the F/A-18 Hornet that alerts pilots when enemy radar is searching for, tracking, or locking onto them. The tones vary with the type and urgency of the threat, which is why they sound so recognisable to aviation fans. Clips of these warnings have spread through flight simulation videos, combat edits, and military documentaries, where they are used as shorthand for aerial danger even when no real aircraft is shown.