Abstract: An implantable medical device that is configured to be exposed to magnetic fields includes a lead, a detection module, a field measurement sensor, and a control module. The lead includes electrodes that are positioned within a heart to sense cardiac signals of the heart. The detection module monitors the cardiac signals to identify cardiac events based on the cardiac signals. The field measurement sensor measures a magnetic field. The sensor generates a field measurement based on the measured magnetic field. The sensor remains in an unsaturated state when exposed to the magnetic field of at least 0.2 Tesla. The control module identifies a presence of the magnetic field based on the field measurement of the sensor and switches operation of the detection module to an MR safe mode based on the field measurement.