The technologies used in the electronic monitoring of offenders continue to develop, and next-generation “tags” will likely feature new capabilities. As the technology becomes more powerful, older criminal justice institutions and practices may appear increasingly anachronistic in one form or other, and their legitimacy called into question. Electronic monitoring systems may appear progressive alternatives to older forms of punishing. However, given the surveillant and controlling qualities of electronic monitoring systems, extending their use is in many respects troubling. This article seeks to examine the electronic monitoring of offenders in the light of the concepts of “penal moderation” and “penal excess”, as well as to reflect on this sanction at the interface of the academic fields of the sociology of punishment and surveillance studies. It is argued that issues relating to intended aims and actual effects of the electronic monitoring of offenders go to the heart of contemporary debates and contradictions regarding penal purpose, the effects of the criminal justice system, electronic surveillance, and explanations of penal change.