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Gas production and consumption is a direct consequence of microbial activity in environmental and industrial settings. In closed batch cultivations, headspace pressure changes therefore give valuable insights into the microbial metabolism. For laboratory scale anaerobic batch cultivations, manual manometer measurements are routinely applied, as a simple and robust method, but it is labour intensive, causes disturbances in the headspace gas and temperature, leading to suboptimal growth, inhibition and noisy data. We built and tested an automated online pressure sensor for closed batch cultivations. It is designed for microbial cultivation and integrates with sterile and anaerobic cultivation workflows. The system uses an absolute pressure sensor (0-30 bar) mounted on a custom designed PCB, with a gas-tight needle mount. An ESP32 microcontroller logs pressure and temperature locally and generates a Wi-Fi access point for real-time visualization and direct CSV download through a local homepage. We detail hardware and software design decisions, assembly, and validation including long-term stability. Case studies demonstrate the applicability for: a multiphasic biogas kinetics during anaerobic digestion, capturing gas uptake dynamics and metabolic shifts during syngas fermentations and co-feeding experiments, and long-term robustness in a multi-year monitoring of a compressed-air system. More than 130 individual sensors have been deployed over 3 years in laboratories, at various academic and industrial settings. The platform provides reproducible, high-resolution pressure measurements that enable calculation of gas formation/consumption rates and improve experimental throughput without disturbing cultures. Design files, firmware, and example analysis scripts are openly available to support adoption and further development.