Computing and digital technology, have transformed many industries. While the transformations in health and medicine have been slow to be realized, the digitization of our lives has created opportunities to better monitor and assess health. Current work on digital biomarkers suggest they may offer a whole new window into understanding disease trajectories and treatment effects. While the opportunities in this area great, there remain challenges to realizing digital biomarkers for adoption in health. This talk will focus on some of the promise and challenges in the development of functional digital biomarkers. The talk will highlight the challenges of developing and validating markers within the constantly challenging digital landscape, as well as exploring the line between monitoring digital biomarkers and surveillance.