This dataset contains all supplementary design, schematic, firmware and analytical materials associated with the prototype described in the article “Hydrostatic Water Displacement Sensing for Continuous Biogas Monitoring.”It provides the complete mechanical assembly in SolidWorks Pack & Go format, a CAD-generated non-final bill of materials, the supplementary pricing table (Table S1), and the full electronic design in the form of the native EasyEDA project together with PDF and PNG schematic exports. The package further includes the Arduino/ESP32 firmware exported from Arduino Cloud, as well as all measurement datasets used for the 24-hour and 90-hour stability tests. To ensure full reproducibility of the figures published in the manuscript, Vega plotting scripts are also provided. The files are intended to support reproduction, verification and further development of the hydrostatic biogas monitoring system in other laboratories or research environments.For additional information, alternative file formats (such as STEP exports), or further support, please contact marekhabara@gmail.com.