In this letter, we analyze experimentally the responsivity of vertical-cavity surface-emitting lasers (VCSELs) to backscattered Doppler radiation. Their responsivity is strongly enhanced by at least 10 dB with the selection of one polarization state in the detection beam and by the presence in VCSELs of polarization bistability. When the VCSELs are operated inside the bistable region, they emit square wave pulses at the Doppler shift frequency in both polarization states. When they are operated outside the bistable region, they emit the normal saw-tooth pulses in both polarization states. These unique features, absent in conventional edge-emitting lasers, make them suitable for new applications in laser Doppler velocimetry (LDV).