While commitment devices such as defaults and direct deposits from wages have been found to be highly effective to increase savings, they are unavailable to the millions of people worldwide who not have a formal wage bill. Self-help peer groups are an alternative commitment device that is widespread and highly accessible, but there is little empirical evidence evaluating their effectiveness. We conduct two randomized field experiments among low-income micro-entrepreneurs in Chile. The first experiment finds that self-help peer groups are very potent at increasing savings. In contrast, a more classical measure, a substantially increased interest rate, has no effect on the vast majority of participants. A second experiment is designed to unbundle the key elements of peer groups as a commitment device, through the use of regular text messages. It finds that surprisingly, actual meetings and peer pressure do not seem to be crucial in making self-help peer groups an effective tool to encourage savings.