A device comprises at least one pair of excitation electrodes forming a capacitor; a floorplan (e.g., a ground plane); and an electronic circuit. The device comprises at least one control electrode arranged at a distance from the capacitor. A switching circuit, of the device, comprises a switch having an open state and a closed state. The switching circuit is designed to apply, to the control electrode, an electric potential common to the floorplan when the switch is in the closed state. The switching circuit is also designed to leave a floating electrical potential for the control electrode when the switch is in the open state. The electronic circuit is designed to measure the mutual capacitance between the pair of excitation electrodes when the switch is in the open state and when it is in the closed state.