A wearable assembly comprising: a wearable article comprising a sensing component (223, 225), wherein the sensing component (223, 225) is one or more electrodes (223, 225) for monitoring an ECG signal of a wearer; an electronics module arranged to be removably coupled to the wearable article, the electronics module comprising: a housing comprising a top surface and a bottom surface; a processor disposed within the housing; an interface element (111, 121, 123) arranged to interface with the sensing component (223, 225) of the wearable article so as to receive signals from the sensing component (223, 225) and provide the same to the processor, wherein the interface element (111, 121, 123) extends through the bottom surface of the housing; and a sensor arranged to monitor a property of the environment external to the electronics module through the housing; characterised in that: the sensor comprises an optical sensor comprising a photoplethysmography, PPG, sensor module for monitoring PPG signals of the wearer; the sensor is disposed within the housing proximate to the bottom surface; and the housing comprises a window aligned with the sensor such that the sensor has line of sight through the window. a wearable article comprising a sensing component (223, 225), wherein the sensing component (223, 225) is one or more electrodes (223, 225) for monitoring an ECG signal of a wearer; an electronics module arranged to be removably coupled to the wearable article, the electronics module comprising: a housing comprising a top surface and a bottom surface; a processor disposed within the housing; an interface element (111, 121, 123) arranged to interface with the sensing component (223, 225) of the wearable article so as to receive signals from the sensing component (223, 225) and provide the same to the processor, wherein the interface element (111, 121, 123) extends through the bottom surface of the housing; and a sensor arranged to monitor a property of the environment external to the electronics module through the housing; characterised in that: the sensor comprises an optical sensor comprising a photoplethysmography, PPG, sensor module for monitoring PPG signals of the wearer; the sensor is disposed within the housing proximate to the bottom surface; and the housing comprises a window aligned with the sensor such that the sensor has line of sight through the window. a housing comprising a top surface and a bottom surface; a processor disposed within the housing; an interface element (111, 121, 123) arranged to interface with the sensing component (223, 225) of the wearable article so as to receive signals from the sensing component (223, 225) and provide the same to the processor, wherein the interface element (111, 121, 123) extends through the bottom surface of the housing; and a sensor arranged to monitor a property of the environment external to the electronics module through the housing; characterised in that: the sensor comprises an optical sensor comprising a photoplethysmography, PPG, sensor module for monitoring PPG signals of the wearer; the sensor is disposed within the housing proximate to the bottom surface; and the housing comprises a window aligned with the sensor such that the sensor has line of sight through the window. the sensor comprises an optical sensor comprising a photoplethysmography, PPG, sensor module for monitoring PPG signals of the wearer; the sensor is disposed within the housing proximate to the bottom surface; and the housing comprises a window aligned with the sensor such that the sensor has line of sight through the window.