Measurements of the resistive component of the leakage current are based on the analysis of the third harmonic component of the total leakage current. Leakage current is measured using a current transformer. The sensor periodically wakes up and performs measurements and analysis of currents. It compares the results with the pre-set values and in case of exceeding sends the information about the unsuitable arrester to the control center. Leakage current is measured using a current transformer. The figure shows the diagnostic information of the surge arrester in the form of an SMS message during development testing, which was performed on a prototype ISOP sample with remote (GSM) communication. The sample was tested on a current surge generator in our own HV laboratory.