In this paper, we provide a comprehensive description of cost-efficient, innovative and interoperable ocean passive acoustics sensors systems, developed within the European FP7 project NeXOS (Next generation Low-Cost Multifunctional Web Enabled Ocean Sensor Systems Empowering Marine, Maritime and Fisheries Management), which can be deployed both on fixed and mobile platforms. Within this context, we designed and developed two passive acoustic sensors, A1 and A2, as new embedded passive acoustic device, low power, and innovative digital hydrophone systems. An important part of the effort is focused on the need for greater dynamic range and the integration on autonomous platforms, such as gliders and profilers. A1 is a standalone small, compact, low power, low consumption digital hydrophone with embedded pre-processing of acoustic data, suitable for mobile platforms with limited autonomy and communication capability. A2 consists of four A1 digital hydrophones with Ethernet interface and one master unit for data processing, enabling real-time measurement of underwater noise and of several soundscape sources.