As acoustic pollution in the oceans is increasing, it is becoming more important to monitor it, with special attention on its effects on the behaviour of cetaceans. In the near future governments may require constant monitoring during sea construction projects or operations. One major construction activity in the coming years will be the construction of wind farms. Not only will these farms produce a constant low level noise in their direct environment while operating, but the building of the foundations necessary to support the wind mills will produce impulsive noise dangerous to any cetaceans in the area and lethal to, for example, fish larvae. For these reasons, noise monitoring has become one of the objectives of the European Seafloor Observation Network (ESONET), to investigate the level of noise produced around European coastlines and its impact on the environment and cetaceans especially. Presented is the architecture for noise and marine mammal monitoring as it is currently implemented in ESONET through the LIDO (Listening to the Deep Ocean Environment) project. LIDO will detect in real-time changes in the background noise levels and register acoustic events (natural, biological and anthropogenic), and identify and track the sources when possible. As the system will be implemented in varying environments, a modular design is used that can be adapted easily, based on local requirements. While the system will most often run from a shore station, a more limited version is developed that can run autonomously with minimal power requirements.