The unrestrained monitor reduces monitoring load, but the variety of physiological values is limited. We propose a new method for measuring oxygen desaturation frequency by analyzing Cheyne-Stokes-like breathing curves based on the fact that the characteristic pattern of the curve occurs at a high probability at oxygen desaturation. We confirmed the effectiveness of our proposal in experiments on patients with sleep apnea and other disorders. This proposal is applicable to any sensors that monitor breathing curves and in calculating physiological values using unrestrained monitors at home and in screenings examination at hospitals having no special equipment.