You know birds have magnetic proteins in the retina, which they use to navigate with. There might be one or two people with a genetic defect that allows them to have the same protein, so they might have some ability to sense magnetic field. Thus you might have one in a million who can sense magnetic slow changing fields, though you do need a large field, and they would also be disorientated by cars, speakers, fridge doors, passing ships, bridges, railways, large buildings and anything with large ferrous concentrations.