Abstract: In response to the problems of long manual temperature measurement cycles and delayed defect detection for transmission lines, an automatic alarm device for transmission line drainage plate heating has been developed. It uses a pressure ring-type thermocouple to collect temperature data and uses a GSM module to send text messages to operation and maintenance personnel. After application testing on transmission lines, the alarm success rate is 100%, the false alarm rate is less than 5%, and the error is less than 1%, improving the reliability of power supply.