A single wearable apparatus for detecting the onset of hypoglycaemia in a subject, the apparatus including: an attachment means to allow the apparatus to be worn on an arm or a leg by the subject; a processor; a memory; one or more output devices; one or more input devices including a sensor comprising an accelerometer for measuring physiological tremor in a subject; and an analysis module for analysing a physiological tremor signal from the sensor over a first period of time to determine the tremor signal power and for storing a predetermined baseline, wherein each tremor signal power value correlates with a blood glucose level of the subject, and generating an alarm signal to initiate an alarm to alert the subject of the onset of hypoglycaemia based solely on detecting a change in the physiological tremor signal indicative of the onset of hypoglycaemia in the subject using the one or more output devices, wherein either the analysis module includes the processor, or the memory is configured with suitable instructions that can be executed by the processor to perform the analysis by the analysis module and generate the alarm signal, and wherein the change in the physiological tremor signal is an increase in tremor signal power of at least 50% relative to a reference tremor signal power value, wherein the reference tremor signal power value is the predetermined baseline and is either preprogrammed, determined based on physiological data of the subject, or determined by a calibration process performed by the analysis module using the one or more input devices and corresponds to a blood glucose level for the subject within a normal range. an attachment means to allow the apparatus to be worn on an arm or a leg by the subject; a processor; a memory; one or more output devices; one or more input devices including a sensor comprising an accelerometer for measuring physiological tremor in a subject; and an analysis module for analysing a physiological tremor signal from the sensor over a first period of time to determine the tremor signal power and for storing a predetermined baseline, wherein each tremor signal power value correlates with a blood glucose level of the subject, and generating an alarm signal to initiate an alarm to alert the subject of the onset of hypoglycaemia based solely on detecting a change in the physiological tremor signal indicative of the onset of hypoglycaemia in the subject using the one or more output devices, wherein either the analysis module includes the processor, or the memory is configured with suitable instructions that can be executed by the processor to perform the analysis by the analysis module and generate the alarm signal, and wherein the change in the physiological tremor signal is an increase in tremor signal power of at least 50% relative to a reference tremor signal power value, wherein the reference tremor signal power value is the predetermined baseline and is either preprogrammed, determined based on physiological data of the subject, or determined by a calibration process performed by the analysis module using the one or more input devices and corresponds to a blood glucose level for the subject within a normal range.