In this article, I explore knowledge practices in increasingly digitized, data-driven, and personalized health-care settings by empirically focusing on the “looper community” in type 1 diabetes. This community develops and uses open-source automated insulin delivery systems and frequently criticizes slow innovation cycles and data monopolies of commercial device manufacturers. Departing from the literature on patient knowledge, I argue that studying these knowledge practices at the intersection of digitized and personalized health care, open-source innovation, and patient activism calls for an expansion of the theoretical notions of patient knowledge. Empirically I map out three knowledge practices: technical, including maintenance and repair work; recursive, including the building and maintenance of adjunct care and support structures; and methodological, including scientistic forms of self-experimentation. I propose “elaborative tinkering” to foreground the nuances of when and how patients’ different forms of knowledge practices intertwine and when they are kept apart. This approach offers new concepts for understanding what it means to know as patients in spaces of (chronic) self-care, innovation, and activism.