This paper reviews recent advances of technologies using radar sensor to detect vital sign of a human subject. A number of front-end architectures, detection methods, and system-level integrations have been reported to improve the detection accuracy and enhance the system robustness. The advantages of noncontact vital sign detection draw lots of attention in various applications, such as health-care monitoring and rescue searching. Several portable systems and integrated circuits have been demonstrated recently. Different system architectures, baseband signal processing, system-level integration and potential applications are compared. Integrating the radar chip to achieve compact size, lower power consumption with signal processing techniques to increase the detection accuracy will continuously be the focus for the researchers in the future.