Detection of live-human presence under the debris is a critical problem especially after natural disasters such as earthquakes and landslides. If a radar system can detect breathing and heartbeats, it would be invaluable and preferable to existing acoustic or ultrasound based systems. Human breathing and heartbeats have very low frequency components and their detection in the presence of noise pose a great challenge for researchers. In this study, we first analyzed the radar parameters for such detection, built a system prototype based on continuous-wave Doppler radar, and tested on human subjects behind concrete walls. Our zero-intermediate-frequency receiver system was able to detect breathing and heart pulses from a 40 cm stand-off distance, behind a 25 cm thick-concrete wall using 7 dBm (5 mW) transmit power.