The arrester online monitor (also known as arrester leakage current and action recorder) is an instrument used in conjunction with zinc oxide arresters in high-voltage AC power systems. The instrument is connected in series in the surge arrester grounding circuit. The mA meter in the monitor is used to monitor the leakage current (peak value) through the arrester under the operating voltage, which can determine whether the arrester is damp and whether the components are abnormal; the action counter records the number of overvoltage actions of the arrester.