Abstract: A sensor and method for indicating the presence of a low magnetic field using high critical temperature superconductor ceramic material is comprised of a sensing element consisting essentially of the high critical temperature superconductor ceramic material without the need for further processing. The sensing element is cooled to a temperature below the critical temperature of the superconductor material, whereby the sensing element becomes superconducting. Electromagnetic energy is applied to the sensing element, a first portion of the energy being absorbed by the sensing element. The amount of the energy absorbed by the sensing element is detected. The sensing element is modulated to provide a reference signal and is biased to a predetermined absorption reference value, whereby a magnetic field of about 10.sup.