The integration of radar-based sensing technology into digital devices, non-digital physical objects, and living environments, from smart desks to smart rooms, offices, and buildings, offers a standardised technical approach to implementing always-available natural interactions, particularly those based on presence, proximity, movement, and gesture input, for ubiquitous computing application scenarios. In the context of smart buildings, as interconnected ecosystems comprising users, devices, non-digital objects, and architectural elements, this chapter draws on the established principles of Ambient Intelligence to introduce a taxonomy of possible spatial locations for radar integration into the living environment. To this end, several application scenarios and their corresponding spatial contexts are examined, including home entertainment in living rooms, professional activities in offices and meeting rooms, and interactions for indoor navigation in smart buildingsSmart buildings. Furthermore, this chapter explores the interaction possibilities enabled by radar-based sensing at multiple levels within a smart building, ranging from integration into small objects at the human scale, such as remote controls, to surfaces and furniture at the room scale, and entire hallways and corridors at the building scale, respectively.