Distance tracing pulsators in binary systems

Classic cepheides and RR Lyr variables are among the most important elements of the space distance scale due to period - metallicity - luminosity relations. Lack of known pulsators with accurate trigonometric parallaxes, the calibration of these relations remains an open problem. We discuss prospects of discovery and investigation of pulsators in binaries of certain observational types which may help obtain its distances. That would establish precise zero-point of the period - luminosity relations.