Detection of magnetic fields associated with corrosion currents provides a new concept for corrosion monitoring. We have used superconducting quantum interference device (SQUID) magnetometry to study the corrosion of the Co-Cr-Mo alloy in a hemispherical water layer. Corrosion was initiated by the introduction of oxygen gas. The SQUID responded systematically to oxygen-alloy interactions, indicating the presence of corrosion-induced magnetic fields. Also, an immediate magnetic field change was observed when liquid phase contacted the metal one provided both phases were of different temperatures. Such a magnetic field generation by the metal/liquid interface was explained in terms of internal thermoelectric currents.