A formal theory for the development of a generic model of an autonomous sensor is proposed and implemented. An autonomous sensor not only interprets the acquired data in accordance with an embedded expert system knowledge base, but is also capable of using this data to modify and enhance this knowledge base. Hence, the system is capable of learning and thereby improving its performance over time. The main objective of the model is to combine the capabilities of the physical sensor and an expert operator monitoring the sensor in real-time. The system has been successfully tested using various simulated data sets and a real thermistor that has been developed as an autonomous sensor.