In a hearing aid with a magnetic field-controlled switch and a method for operating such a hearing aid, the magnetic field sensor for automatically switching the hearing aid is miniaturized and made more cost-effective by the use of a ferrite component as the magnetic field sensor. This component can be evaluated by a Wheatstone bridge circuit which is fed by an oscillator. In this context, a measuring amplifier with a threshold value detector supplies a corresponding switching signal for the hearing aid.