In the field of Earth System Science, the comprehensive understanding of complex spatio-temporal environmental processes and the prediction of future trends rely heavily on careful data collection, analysis, and interpretation. And in particular time series data from sensor systems play a central role in revealing patterns, identifying changes, evaluating model systems and, ultimately, guiding decision making in various environmental domains. But despite the availability of dedicated time series databases to support the development of time series management systems, it has been recognized that also the collection, management, and provision of associated sensor metadata is crucial for ensuring sensor data usability and interpretability. In this context, the four Helmholtz Centers UFZ, GFZ, FZJ, and KIT from the Research Field Earth and Environment jointly develop a dedicated open-source platform for enabling a FAIR and consistent management of such precious sensor metadata - the so-called Sensor Management System (SMS). This system supports scientists and technicians in the harmonized and user-friendly management of sensors, measurement setups, and campaigns. It features a modern and user-friendly interface coupled with a robust JSON:API and supports the OGC SensorML standard for data exchange. It includes an OAuth-based authentication system using the Helmholtz AAI, complemented by a sophisticated rights management structure. Sensor attributes within SMS adhere to a unified metadata catalog that includes mandatory, optional, and user-specific attributes. The SMS provides traceability and provenance tracking. Interfaces to handle systems such as B2INST allow persistent identifiers to be generated. The SMS is being developed as part of the DataHub, an initiative that implements a uniform and FAIR research data infrastructure across the seven Helmholtz Centers of the Research Field Earth and Environment. Presently operational at GFZ (https://sensors.gfz-potsdam.de), UFZ (https://web.app.ufz.de/sms/), FZJ (https://sms.earth-data.fz-juelich.de/), and KIT (https://sms.atmohub.kit.edu/), the Sensor Management System provides a decentralized solution. For those choosing self-hosting, comprehensive documentation is available (https://hdl.handle.net/20.500.14372/SMS-Readme). Users seeking guidance on system navigation and features can refer to the WIKI (https://hdl.handle.net/20.500.14372/SMS-Wiki) for a user-centric guide and valuable insights into seamless utilization.