This letter presents an ultrawideband (UWB) radar for occupancy and vital signs detection. The proposed burst-chirp operation achieves > 30\times power reduction and abundant margin for the UWB spectrum regulations. With the proposed Domino chirp generation and time-domain predistortion, the radar has a fast chirp slope of 0.7 GHz/40 μ \text{s} and a low RMS error of 0.5 MHz. Fabricated in a 40-nm CMOS process, the presented radar consumes a record-low power of 680 μ \text{W} and can detect human respiration and heartbeat up to 15 and 5 m, respectively.