A method and a device for a galvanically isolated AC/DC-sensitive measurement of a residual current (ΔI), includes a component sensitive to magnetic fields which switches between at least two states in the course of oscillation. A magnetic field is formed in a sphere of action of the component sensitive to magnetic fields due to the residual current (ΔI) and an oscillator signal that switches between a state 1 and a state 2. As a function of the residual current-driven magnetic field, times of stay of the oscillator signal occurring in states 1 and 2 are determined and an output signal proportional to the residual current is obtained from the ratio of the times of stay.