Noise. It is around us, everywhere, all the time. It is hard to control, hard to shut out. It affects our health, sometimes even without us noticing it. Noise is one form of pollution, and is causing annoyance and other health effects. Therefore, the Norwegian government set a national goal to reduce noise pollution from 1999 levels by 10% until 2020, but this process is not going as well as it should. The motivation of this project is to help reach the goal by highlighting areas that need most attention. The goal of this thesis is to explore a novel approach to measuring outdoor noise levels, with better spatial and temporal coverage. In the current approach, professionals use high quality equipment to measure a smaller area, then extrapolate from this data. This method potentially ignores other noise sources and amplifying or attenuating effects of the environment. In addition, it is quite costly. In contrast, my approach delegates the task to local citizens, and leverages the powerful and ubiquitous smartphones. An application runs in the background and repetitively measures the noise level, processes and uploads it to a server. There it is aggregated and displayed as a noise map to anybody interested.