Mobile devices have begun to raise questions around the potential for overuse when in the presence of family or friends. As such, we conducted a diary and interview study to understand how people use mobile devices in the presence of others at home, and how this shapes their behavior and household dynamics. Results show that family members become frustrated when others do non-urgent activities on their phones in the presence of others. Yet people often guess at what others are doing because of the personal nature of mobile devices. In some cases, people developed strategies to provide a greater sense of activity awareness to combat the problem. Mobile phone usage was sometimes perceived as beneficial by providing a mechanism for needed disengagement from family members. These findings suggest several opportunities for redesigning mobile device software to mitigate emergent frustrations, and open up new opportunities for nurturing social interactions among family members.