Abstract: A detector for a magnetic field having a low frequency compared to background EMF and having a magnitude approximately 1,000 times less than the EMF, the detector comprising: a pickup coil for capturing the magnetic field and the background EMF; an integrator coupled for receiving a signal having respective components representative of the magnetic field and the background EMF, the integrator having a time constant such that successive positive and negative polarity portions of the component representative of the background EMF cancel out one another in the integrator, but the component representative of the magnetic field results in a net output signal from the integrator, the net output signal being indicative of the magnitude of the magnetic field; and, a magnetic field strength output indicator responsive to the net output signal from the integrator, whereby the magnetic field can be detected with great sensitivity notwithstanding the background EMF.