In an increasingly technology-textured environment, smart, intelligent and responsive technology has moved onto the body of many individuals. Mobile phones, smart watches, and wearable activity trackers (WATs) are just some of the technologies that are guiding, nudging, monitoring, and reminding individuals in their day-to-day lives. These devices are designed to enhance and support their human users, however, there is a lack of attention to the unintended consequences, the technology non-neutrality and the darker sides of becoming human-tech hybrids. Using the extended mind theory (EMT) and agential intra-action, we aimed at exploring how human-tech hybrids gain collective skills and how these are put to use; how agency is expressed and how this affects the interactions; and what the darker sides are of being a human-tech hybrid. Using a qualitative method, we analyzed the experiences of using a WAT, with a specific focus on how the tracker and the individual solve tasks, share competences, develop new skills, and negotiate for agency and autonomy. We contributed with new insight on human-tech hybridity and presented a concept referred to as the agency pendulum, reflecting the dynamism of agency. Finally, we demonstrated how the EMT and agential intra-action as a combined theoretical lens can be used to explore human-tech hybridity.