The iPhone bionic pancreas has been used in earlier studies, during which volunteers used the system for up to 11 days at a time while living their normal lives at home and work. The iLet bionic pancreas has never been tested in humans. In this new study, volunteers will participate in a training visit to learn how both devices work. They will then use the iPhone-based BP for 1 day and the iLet BP for 1 day in random order using Lilly glucagon. They will then use the iLet BP for one additional day using Xeris Xerisol glucagon (a stable formulation of human glucagon).