Heart monitors, step counters, sleep recorders—technology that monitors human biological activity has become ubiquitous. Scholars have been following the emergence of this quantified health self, enabled by digital devices, since its inception, but debates around the moral limits of health surveillance have assumed a new prominence in the wake of the pandemic. The development of apps for diagnosing, tracing, and tracking infected persons, through smart devices they already own, has made the intersection between private and public health surveillance extremely vivid. This postdoctoral project investigates the use of health-apps as a performance of the biological self that hinges on specific social and cultural relationships. The research is carried out in Britain, where the person as an object of health characteristics has been a profound form of social recognition since the foundation of its National Health Service.