As urbanization accelerates worldwide, public safety has become a critical indicator for sustainable urban development. Traditional crime prevention through environmental design (CPTED) primarily focuses on static physical changes, which often fail to respond flexibly to dynamic crime patterns in smart cities. We propose a new intelligent sensor-integrated CPTED framework to overcome these limitations. By analyzing global leading cases in Singapore, Barcelona, and South Korea, we establish a three-layer digital CPTED framework consisting of a physical layer, a sensing layer, and an integration layer. The physical layer emphasizes the material properties of sensor housings and enclosure design to ensure durability in harsh environments. The sensing layer focuses on multimodal data fusion and edge computing for real-time preprocessing. The integration layer enables immediate physical feedback to urban facilities through integrated platforms. Furthermore, the study provides technical guidelines, including a geometric analysis of the detection area and measures for securing hardware reliability. This multidisciplinary model, merging engineering sensor systems with urban design, contributes to establishing safety standards and efficient operation systems for future smart cities.