A wearable assembly comprising: a wearable article comprising a sensing component , wherein the sensing component is one or more electrodes 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 arranged to interface with the sensing component of the wearable article so as to receive signals from the sensing component and provide the same to the processor , wherein the interface element 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 , wherein the sensing component is one or more electrodes 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 arranged to interface with the sensing component of the wearable article so as to receive signals from the sensing component and provide the same to the processor , wherein the interface element 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 arranged to interface with the sensing component of the wearable article so as to receive signals from the sensing component and provide the same to the processor , wherein the interface element 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. <EOS>