In this paper, we study how a displacement of a quantum system appears under a change of relativistic reference frame. We introduce a generic method in which a displacement operator in one reference frame can be transformed into another reference frame. It is found that, when moving between noninertial reference frames, there can be distortions of phase information, modal structure, and amplitude. We analyze how these effects affect traditional homodyne detection techniques. We then develop an in-principle homodyne detection scheme which is robust to these effects, called the ideal homodyne detection scheme. We then numerically compare traditional homodyne detection with this in-principle method and illustrate regimes when the traditional homodyne detection schemes fail to extract full quantum information.