This article focuses on the ways in which a flash glucose monitoring system, FreeStyle Libre®, is introduced and used by people living with type 1 diabetes, their relatives and healthcare professionals. It draws on a multi-sited ethnography in a variety of clinical and daily situations, and on interviews with caregivers and people living with diabetes. We explore how the users develop knowledge-in-practice, and consider the use of self-management technologies to be largely dependent on locally grounded and situated care acts, and resulting from the relational, pragmatic and creative maneuvering of technology-in-practice. Our findings show that adjustments between users, their bodies and the technology are required, and show the reflexive work and practices of patients and relatives who learn to use the device in a proper way. Moreover, we reveal that practitioners see this technology as a tool that not only improves self-care practices but also clinical practices, and that wearing and using this new medical device may become a moral injunction for self-improvement. Our results illustrate the techno-social reconfigurations at work and the development of new ways of feeling, thinking and acting in diabetes (self-) care.