Sedentary lifestyle and lack of physical activity are well-established risk factors for chronic disease and adverse health outcomes. Thus there is enormous interest in measuring physical activity in biomedical research. Many consumer physical activity monitors, including Basis® Health Tracker, BodyMedia® Fit, DirectLife®, Fitbit® Flex, Fitbit One, Fitbit Zip, Garmin® Vivofit, Jawbone® UP, MisFit® Shine, Nike® FuelBand, Polar® Loop, Withings® Pulse O2, and others have accuracies similar to that of research-grade physical activity monitors for measuring steps. This review focuses on the unprecedented opportunities consumer physical activity monitors offer for human physiology and pathophysiology research because of their ability to measure activity continuously under real life conditions and because they are already widely used by consumers. We examine current and potential uses of consumer physical activity monitors as a measuring or monitoring device, or as an intervention in strategies to change behavior and predict health outcomes. The accuracy, reliability, reproducibility, and validity of consumer physical activity monitors is reviewed, as are limitations and challenges associated with using these devices in research. Other topics covered include how smartphone apps and platforms such as the Apple ResearchKit can be used in conjunction with consumer physical activity monitors for research. Lastly, the future of consumer physical activity monitors and related technology is considered: pattern recognition, integration of sleep monitors, and other biosensors in combination with new forms of information processing.