This essay is about the importance of sound and music in science fiction and horror films. An introduction to filmmusic in general is included and also a view of the use of specific themes in films, such as the wellknown melody in Jaws. The focus of the essay is particulary the two first films in the Alienseries, who are analysed in regard to their use of sound and music. Michel Chions theories of the three different modes of listening (the causal, the semantic and the reduced) is presented and applied to Alien and Aliens. The purpose is to show that sound and music in the genre have a large influence on the audience and that there are more to the Alienduo than visual fear. Key words: science fiction, horror, sound, Chion