Stress is the body’s defensive mechanism for addressing social and environmental threats and stimuli. Most reactions to stress are controlled by the autonomic nervous system and operate unconsciously. As chronic stress is acknowledged as a risk factor for mental illnesses and disease states, including cardiovascular disease, efforts to detect, address, and reduce stress can lead to improved health outcomes. Heart rate variability, a measure of the variation in time between adjacent heartbeats, can serve as a useful proxy for measuring stress; research has shown that low variability is associated with high stress. Photoplethysmography, an optical method for measuring changes in blood volume in a bed of tissue, is an effective and accurate way to measure HRV and therefore detect moments of stress. Equipped with medical-grade PPG functionality, the Vyvo LifeWatch provides highly useful method for measuring stress to help users protect their health.