Each beat of your heart or burst of brain activity relies on tiny electrophysiological currents that generate minuscule ripples in the surrounding magnetic field. These field variations provide the basis for a range of research tools and diagnostic techniques with mouthful names like magnetoencephalography (MEG) and magnetocardiography (MCG). But tapping into biology’s faint magnetic fields requires heroic and costly measures, including high-tech shields to block the larger, potentially confounding magnetic forces all around us and boutique magnetic field sensors that require expensive and cumbersome liquid helium cooling.