A wearable device is disclosed. The wearable device comprises an ambient temperature sensor, an ambient humidity sensor, an ultraviolet detector, a skin temperature sensor, an alarm module and a process unit. The ambient temperature sensor, the ambient humidity sensor and the ambient humidity sensor detect an ambient temperature, an ambient humidity and an ultraviolet index nearby the wearable device, respectively. The skin temperature sensor contacts with the users skin and detects a skin temperature of the user. The process unit stores at least one preset heatstroke condition and determines whether heatstroke occurs based on the detected results of the ambient temperature, the ambient humidity, the ultraviolet index and/or the skin temperature and the at least one preset heatstroke condition. The alarm module is enabled by the process unit to generate at least one alarm signal when the process unit determines that the at least one preset heatstroke is met.
