Numerous functionalities are provided by smartphones and prolonging their battery lifetime is an undeniably critical support issue. In this paper, we propose a low-power scheme called unnecessary region freezing (URF) that achieves significant total power consumption reduction in smartphones by reducing unnecessary drawing computation that originates from a user's uninteresting display region. We implement URF on a real smartphone (Nexus 6). Then, we evaluate our scheme on top of an existing low-power scheme, partial display darkening (PDD). The results indicate that the URF scheme reduces total power consumption by average 5.1% through 12.5% depending on the size of the unnecessary region, compared with the PDD scheme.