A measuring device configured to detect a metal object includes two emission coils configured to produce superimposed magnetic fields. The measuring device also includes a device configured to determine a differential voltage between the emission coils. The measuring device further includes a control device configured to supply the emission coils with alternating voltages such that the value of an AC voltage component of the differential voltage, which is time synchronized with the alternating voltage, is minimized. The control device is configured to detect the metal object when the ratio of the alternating voltages does not correspond to the ratio of the impedances of the emission coils when the metal object is not there.