Smart cities are now an established area of technological development and theoretical inquiry. Research on smart cities spans from investigations into its technological infrastructures and design scenarios, to critiques of its proposals for citizenship and sustainability. This article builds on this growing field, while at the same time accounting for expanded urban-sensing practices that take hold through citizen-sensing technologies. Detailing practice-based and participatory research that developed urban-sensing technologies for use in Southeast London, this article considers how the smart city as (...) a large-scale and monolithic version of urban systems breaks down in practice to reveal much different concretizations of sensors, cities, and people. By working through the specific instances where sensor technologies required inventive workarounds to be setup and continue to operate, as well as moments of breakdown and maintenance where sensors required fixes or adjustments, this article argues that urban sensing can produce much different encounters with urban technologies through lived experiences. Rather than propose a “grassroots” approach to the smart city, however, this article instead suggests that the smart city as a figure for urban development be contested and even surpassed by attending to workarounds that account more fully for digital urban practices and technologies as they are formed and situated within urban projects and community initiatives. (shrink)