  Advances in voice technology and voice user interfaces (VUIs) -- such as
Alexa, Siri, and Google Home -- have opened up the potential for many new types
of interaction. However, despite the potential of these devices reflected by
the growing market and body of VUI research, there is a lingering sense that
the technology is still underused. In this paper, we conducted a systematic
literature review of 35 papers to identify and synthesize 127 VUI design
guidelines into five themes. Additionally, we conducted semi-structured
interviews with 15 smart speaker users to understand their use and non-use of
the technology. From the interviews, we distill four design challenges that
contribute the most to non-use. Based on their (non-)use, we identify four
opportunity spaces for designers to explore such as focusing on information
support while multitasking (cooking, driving, childcare, etc), incorporating
users' mental models for smart speakers, and integrating calm design
principles.
