An apparatus and method for measuring geomagnetically induced currents (GIC) is disclosed. The apparatus is configured to measure GICs temporarily flowing in high-voltage, 60 Hz power transmission conductors, and includes a securing means for securing the apparatus to the power transmission conductor. The apparatus further includes a flux concentrator having a toroidal ferrite core and winding wound around the core configured to capture a magnetic field from the power transmission conductor; a hall-effect sensor assembly configured to receive the magnetic field from the flux concentrator and produce a voltage signal corresponding to the magnetic field; and an electronics module configured to receive the voltage signal from the hall-effect sensor assembly, conduct measurements, and transmit the measurements to a local access point.