The Acoustic Localization Positioning System is the outcome of several years of participatory development with musicians and artists having a stake in sonic arts, collaboratively aiming for nonobtrusive tracking and indoors positioning technology that facilitates spatial interaction and immersion. Based on previous work on application scenarios for spatial reproduction of moving sound sources and the conception of the kinaesthetic interface, a tracking system for spatially interactive sonic arts is presented here. It is an open-source implementation in the form of a stand-alone application and associated Max patches. The implementation uses off-the-shelf, ubiquitous technology. Based on the findings of tests and experiments conducted in extensive creative workshops, we show how the approach addresses several technical problems and overcomes some typical obstacles to immersion in spatially interactive applications in sonic arts.