An app will come in due time, but new functionality for all platforms is considered more important. The website works great on mobiles too. :)
@CallmeHopelessNotRomantic: I knew that would be your favorite! ^^
@Quizling & rokrchik1211: It does play sounds when SW is not the active tab. It is disabled when you see them pop up to prevent annoyance over time.
@EightDown: It is indeed a feature that was only just added and an option to turn them off has just been confirmed to be added later.