The “secret” radio stations in the City of Buenos Aires The radio spectrum is monitored by international and national bodies. These bodies determine the specific ranges, frequencies and powers for each user - state, private or amateur -, supervising not only technical aspects but also cultural, artistic, legal and administrative aspects. With the return of democracy in Argentina, in 1983, dozens of “clandestine” radio stations began to appear. Since then, their broadcasts have shared the airspace with legal stations. Called ‘pirates’ by radio station licence holders, these alternative, popular, community projects represent numerous voices, most of which are non-profit. Their main targets are the local communities of their neighbourhoods and their locations reflect the socioeconomic distribution of the city. The interference between legality and illegality constitutes the base of this research conducted in Buenos Aires; Invisible occupation attempts to build a map of the city’s airspace through an interactive sound installation, made from recordings of clandestine broadcasts. The temporary occupation of public space is thus focused on through sound, searching for immaterial marks.