An object-sensing device is presented. The device includes a waveguide and a substrate holding a liquid crystal layer, wherein radiation propagates through the waveguide via total internal reflection. A radiation emitting element is positioned along a radiation input surface of the waveguide, and a radiation receiving element is positioned to receive radiation exiting the waveguide. The radiation receiving element may be positioned across the waveguide from the radiation emitting element. Alternatively, the radiation receiving element may be positioned on a surface that contacts the radiation input surface of the waveguide that is optically coupled to the radiation emitting element.