Due to the noncontact and low-cost features of Doppler radar sensors, it has been adopted to detect physiological motion signals in variety applications. This paper introduces two portable Doppler radar sensor devices named as 'iMotion radar' and 'iMotion2 radar'. The iMotion radar is a 2.4-GHz AC-coupled direct-conversion continuous-wave Doppler radar. The iMotion2 radar is designed with the same structure except this version adopts DC coupling method in order to sense motions at very low frequency without frequency-dependence distortions. An additional circuit is designed for iMotion2 to eliminate large DC offset. Both of the two radars have been used in different applications. The experimental results have demonstrated good reliability and flexibility. The details in hardware design are given in this paper and two applications, which are achieved by those radar devices, are reviewed.