The urgency to address the environmental impacts of the building sector, particularly emissions allocated to building operation, necessitates immediate, informed action. Occupant behaviour is a known driver of building operational emissions. Use of Internet-of-Things (IoT) devices holds great potential in mitigating and distributing occupancy-driven energy demand, ultimately aiming for net-zero emissions. However, a full accounting of the environmental impacts and advantages is still lacking. As the adoption of IoT scales up, what will be the environmental impact of the tools used, from sensor life cycle to data storage? This study reviews the interdisciplinary literature on life cycle assessment (LCA) of IoT in buildings, encompassing emissions from pre-deployment to end-of-life, as well as savings from reduced building operational emissions. This opens a vital discourse on the opportunities and challenges of building-related IoT.