A device that measures blood oxygen levels and heart pulse rate in a noninvasive way. It works by emitting two beams of light-one red, the other infrared- and measuring what passes through a thin part of the body or is reflected back from a thick part. From these signals the pulse can be detected, and the amount of oxygen in the blood can be determined. The most common form is a clip that fits over a finger. Such devices are now widely used for home monitoring as well as in clinical practice.