Smart digital infrastructures predicated on myriads of sensors distributed in the environment are often rendered as key to contemporary urban security governance to detect risky or suspicious entities before or during a criminal event takes place. At the same time, they often involve surveillance of urban environments, and thus not only criminals but also large groups of people and entities unrelated to criminal phenomena can end up under close inspection.This chapter makes its contribution on two levels. For one, it offers a theoretical framework to the research and conceptualization of the role of sensing infrastructures in urban security practices. It shows how insights from Philosophy of Technology and Science and Technology Studies can produce a nuanced understanding of the role of digital technologies in security practices, beyond standard conceptualizations of technology. Moreover, the chapter proposes a geological approach to enrich our repertoire of imagining and researching smart urban ecosystems.Secondly, the chapter contributes to a higher level of transparency of these practices by presenting the results of ethnographic research performed in a set of police organizations that employ sensing infrastructures and algorithmic profiling in their practices. The chapter draws empirically on research performed in the Dutch police, both at municipal and national levels with some additional material gathered in a constabulary in England. In these organizations, resource allocation decisions are often predicated on automated number plate recognition technology that processes data from an array of smart cameras distributed in the environment. In these ways together, the chapter highlights a set of normative issues with implications for the effectiveness and legitimacy of urban security (surveillance) practices in smart environments.