A monitoring device (20) for monitoring the vital signs of a user is disclosed herein. The monitoring device (20) is preferably an article (25) having an optical sensor (30) and a circuitry assembly (35). The optical sensor (30) preferably comprises a photodetector (130) and a plurality of light emitting diodes (135). The monitoring device (20) preferably provides for the display of the following information about the user: pulse rate; blood oxygenation levels; calories expended by the user of a pre-set time period; target zones of activity; time; or distance traveled.