The utility model belongs to electric power system transmission line fortune dimension field especially relates to an external damage confession electric alarm is prevented to circuit. The utility model discloses a power supply unit, alarm unit, acquisition unit, the power supply unit is the electric energy that alarm unit and acquisition unit provided work needed respectively, the alarm unit includes audible -visual annunciator, acquisition unit includes infrared sensor, the scanning signal that audible -visual annunciator received infrared sensor realizes reporting an emergency and asking for help or increased vigilance, the power supply unit is solar cell panel. The utility model is suitable for a mechanical construction is carried out at scene under the transmission line line, and thealarm power supply is sufficient to the normal during operation of alarm under to the line circumstances real time monitoring can carry out.