A method of detecting a life includes receiving an echo signal including an in-phase component and a quadrature component, performing a preprocessing procedure on the echo signal to generate a preprocessed signal, generating, according to the preprocessed signal, complex conjugate data associated with the in-phase component and the quadrature component, performing a first time-domain-to-frequency-domain transform on the complex conjugate data to generate Doppler spectrogram data comprising a plurality of positive velocity energies and a plurality of negative velocity energies, generating combined Doppler spectrogram data according to the plurality of positive velocity energies and the plurality of negative velocity energies, performing a second time time-domain-to-frequency-domain transform on the combined Doppler spectrogram data to generate spectrum data, and determining whether a life is detected according to the spectrum data.