In the sound installation Roompiano a grand piano is electromechanically connected to sensors measuring radioactivity. While the individual radioactive decay processes are being transformed into sounds, they establish continuously changing spatial acoustics that follow the rules of contingency. The room, so to speak, plays itself. During the exhibition period a professional player or a laymen is recruited to play the piano for two hours in the morning as well as in the afternoon. The following two pieces are performed. Dialog one : replay the row of three tones you just heard after reading this, played by the room. Stop when the room starts to play the piano, restart when silent. Dialog two : play in the breaks between the tones played by the room, stop as soon as the room starts to play, restart when silent. Due to continuous randomness, soon the central motive of the composition shifts to the rising awareness of the interaction between the piano player and the self-played grand piano.