This research examines the twin transition—ecological and digital—through the study of smart buildings. It analyzes the interplay between technical, social, and spatial dimensions at work in “smart” building projects—buildings that incorporate connected technologies to manage their infrastructure—to explore how these technological systems are integrated by designers into development projects. Smart buildings are inhabited spaces where optimization strategies, environmental imperatives, and the sensory experiences of occupants intersect. A geographical analysis of these spaces allows us to examine the tension between the pursuit of efficiency and the rebound effects caused by these technologies, while shedding light on the reconfigurations of the relationship between designers and users. By drawing on the concept of lived space, this work aims to highlight how the design of energy-efficient buildings reconfigures users’ environments through digital and energy-related mediations.