Current health care is primarily in-clinic, episodic, and semi-empirical. With the development of intelligent devices such as smartphones, smartwatches, and more cutting-edge devices such as in-body devices and contactless in-home sensors, we are beginning to see a paradigm shift in health care. The new paradigm can be summarized under the framework of digital health: health care is becoming more embedded in daily life, using more continuously collected data, and making more data-driven decisions. We will discuss three of our research works about digital health in this thesis: the first one details our system for deep in-body communication and localization using a backscatter scheme, which solves the critical challenges of near-zero-power in-body continuous monitoring. The second one describes our work on digital biomarkers that are developed using passive measurement of in-home unscripted daily gait speed data by our contactless in-home sensors, which shows how this new method of daily continuously-collected health data has the potential to transform the way we assess Parkinson’s disease severity, motor fluctuation, and progression. The final work discusses the application of a wireless non-contact monitoring system for patients with COVID-19, which can be used to remotely monitor their acute and long-term physiological and behavioral symptoms. These three studies on continuous monitoring suggest innovative new directions for the future of digital health.Ph.D.