This paper explores the ways that relationships of mutual monitoring and accountability are being reconstructed and redefined with the widespread uptake of mobile technologies. The paper draws on ethnographic research with young people in the United Kingdom as a case study, and details both the institutional and regulatory monitoring to which teenagers are subject (and which they resist), as well as the mutual monitoring in which teenagers engage amongst themselves. This paper argues that to understand these emerging relations of monitoring, attention must be paid not only to the institutionalized surveillance of social groups by the state or organizations in mobile technologies, but also crucially to mutual self monitoring. "Surveillance" in this sense is contextually located and defined, and continually negotiated and resisted.