A method for safeguarding the health of a user by automatically notifying a personal emergency is applied in a wearable device worn around a user's body or part. The method includes ultrasonic signals being periodically transmitted through the user's body and received by a receiver. A state of health of the user' body is determined according to the ultrasonic signals and a signal notifying a personal emergency is generated if the state of health of the user's body is abnormal. The signal is transmitted to at least one base station, to inform the base station to determine location of the wearable device for assistance-rendering purposes.