Abstract: A monitoring system for monitoring a biological subject including a monitoring device having a housing configured to be attached to or supported by an ear of the subject in use, one or more sensors, the one or more sensors including a photoplethysmogram (PPG) sensor provided in the housing and configured to measure attributes of blood flow within the ear, and a monitoring device processor configured to acquire sensors signals from the one or more sensors and generate sensor data at least partially in accordance with signals from the one or more sensors. A transmitter is provided that transmit the sensor data with one or more processing systems receiving the sensor data, analyzing the sensor data and generating a health state indicator indicative of a health state of the subject.