Device for determining a state variable, comprising: a first element and a second element which are designed to move relative to one another, the first element being an outer ring of a roller bearing and the second element being an inner ring of the roller bearing and partially guiding the current flow through a lubricant; an evaluation unit; a first electrical connection between the evaluation unit and the first element; and a second electrical connection between the evaluation unit and the second element, the evaluation unit being designed to generate an electric current flow between the first element and the second element, to determine an impedance, and to determine the state variable on the basis of the determined impedance or the change thereof, the evaluation unit being further designed to determine at least one of the following state variables on the basis of the determined impedance: a radially or axially acting force, a lubricating film thickness, a change in the lubricant, a speed, a temperature, a degree of aging, a shaft displacement or a load, characterized in that the outer ring or the inner ring has an electrical insulation in order to hold the outer ring so as to be electrically insulated by a bearing seat or to support a rotatable element so as to be electrically insulated from the inner ring so that the electric current flow can flow-undisturbed by the bearing seat or the rotatable element-from the evaluation unit through the roller bearing, the first electrical connection being connected directly to the outer ring and the second electrical connection coupling to the inner ring via at least one of the following couplings: a capacitive coupling, a sliding contact, the capacitive coupling between the evaluation unit and the inner ring of the roller bearing being determined by calibration. a first element and a second element which are designed to move relative to one another, the first element being an outer ring of a roller bearing and the second element being an inner ring of the roller bearing and partially guiding the current flow through a lubricant; an evaluation unit; a first electrical connection between the evaluation unit and the first element; and a second electrical connection between the evaluation unit and the second element, the evaluation unit being designed to generate an electric current flow between the first element and the second element, to determine an impedance, and to determine the state variable on the basis of the determined impedance or the change thereof, the evaluation unit being further designed to determine at least one of the following state variables on the basis of the determined impedance: a radially or axially acting force, a lubricating film thickness, a change in the lubricant, a speed, a temperature, a degree of aging, a shaft displacement or a load, characterized in that the outer ring or the inner ring has an electrical insulation in order to hold the outer ring so as to be electrically insulated by a bearing seat or to support a rotatable element so as to be electrically insulated from the inner ring so that the electric current flow can flow-undisturbed by the bearing seat or the rotatable element-from the evaluation unit through the roller bearing, the first electrical connection being connected directly to the outer ring and the second electrical connection coupling to the inner ring via at least one of the following couplings: a capacitive coupling, a sliding contact, the capacitive coupling between the evaluation unit and the inner ring of the roller bearing being determined by calibration.