In this paper, the development of a fundamentally new, topology-based cable sensor design concept is summarized for crack detection in reinforced concrete (RC) structures. The sensitivity, spatial resolution, and signal loss of sensors are investigated both numerically and experimentally. Two sensors were fabricated and validated with small- and large-scale laboratory tests under different loads. Both were proven sensitive to crack of various sizes from visually undetectable to excessive, giving the location and severity of damage simultaneously. One sensor has been installed on a three-span bridge for its long-term monitoring. It is capable of recording damage that has occurred during a recent event.