As computing moves into every aspect of our daily lives, the values and assumptions that underlie our technical practices may unwittingly be propagated throughout our culture. Drawing on existing critical approaches in computing, we argue that reflection on unconscious values embedded in computing and the practices that it supports can and should be a core principle of technology design. Building on a growing body of work in critical computing, reflective design combines analysis of the ways in which technologies reflect and perpetuate unconscious cultural assumptions, with design, building, and evaluation of new computing devices that reflect alternative possibilities. We illustrate this approach through two design case studies.