The ‘electronic logbook’ (EL) is a penitentiary tool created in 2009 by three prison guards. This software application makes it possible to continually record and intensively circulate information on day-to-day events in prison, generat- ing forms of knowledge on prisoners – key components of behavioural control.1 The prison administration is currently trying to bring the EL into widespread use, arguing that since this system individualises the handling of detained per- sons, its implementation helps bring French prisons into conformance with the European Prison Rules (EPR). At the same time, the EL has been attacked by activists engaging in the ‘legal guerrilla warfare’ (Chantraine and Kaminski, 2007) that in part characterises contemporary militant activism in the prison sphere. Thus, taking advantage of a window of opportunity left open when the prison administration delayed having the tool approved by the Commission nationale de l’informatique et des libertés (CNIL), International Prison Watch lodged an unsuccessful complaint with this body in late 2009, demanding that the system be abrogated, to stop what it viewed as the ‘collection of sensitive personal data [ . . . ] operating outside of any legal framework’.