The present invention relates to a control device for controlling at least one function of a motor vehicle unit. Said control device includes a capacitive sensing surface (2) configured so as to detect a manual command from a user. Said control device is characterized in that it also comprises a device for detecting objects having ferromagnetic properties, said detection device including:—at least one magnetic field generation device (3) configured so as to generate a magnetic field on the capacitive sensing surface (2);—at least one device (4) for measuring the magnetic field generated by the magnetic field generation device (3); and—a device for monitoring the control (5), that is connected to the measurement device (4) and to the capacitive sensing surface (2), and is configured so as to monitor the control signal emitted by the capacitive sensing surface (2) on the basis of the magnetic field measured by the measurement device (4) during detection of the command. The present invention also relates to a method for controlling such a device.