Technologists frequently promote self-tracking devices as objective tools. This book argues that such glib and often worrying assertions must be placed in the context of precarious industry dynamics. The author draws on several years of ethnographic fieldwork with developers of self-tracking applications and wearable devices in New York City's Silicon Alley and with technologists who participate in the international forum called the Quantified Self to illuminate the professional compromises that shape digital technology and the gap between the tech sector's public claims and its interior processes. By reconciling the business conventions, compromises, shifting labor practices, and growing employment insecurity that power the self-tracking market with device makers' often simplistic promotional claims, the book offers an understanding of the impact that technologists exert on digital discourse, on the tools they make, and on the data that these gadgets put out into the world.