Mechanical, electronic, algorithmic, and computer network facets are combined to create a highly integrated advanced sensor that monitors the gas density, state-of-repair, and events associated with switchgear. Measurements of gas pressure, atmospheric pressure, gas temperature, are used with models of the non-ideal behavior of a particular gas to realistically estimate gas density. A hierarchical system of signal processing optimizes measurements working within high-frequency, real-time, short-term, medium-term, diurnal, long-term, and historical timeframes and overcomes measurement errors present in real-world applications. The time at which a condition such as gas density will reach a particular level is calculated. Events such as threshold attainments and switchgear operation are detected. A large memory stores all raw data values allowing flexible re-processing and verification at any future time. Instantaneous as well as logged information is communicated in convenient formats over a selected digital network. An embedded web server provides a familiar graphical user interface.