Subnautica is an underwater survival game developed by Unknown Worlds Entertainment and fully released in 2018. Its time capsules are containers left by other players, containing a short message, a screenshot and a few items to help a new survivor. Finding one on the seabed breaks the game's isolation, which is why the associated chime became memorable for players. Clips of discoveries were shared widely in Let's Plays and short edits, and the sound later spread as a general discovery cue beyond the game itself.