It is difficult to monitor whether information was originally retrieved internally, from our own memory, or externally, from another person or a device. We report two experiments that examined whether people were more likely to confuse prior access to information on a smartphone with accessing their own knowledge. Participants were experimentally assigned to either attempt to answer questions from memory or with a smartphone. One week later, we tested memory for the answers and source memory for the modality of the original attempt to retrieve the answer. Participants exhibited poorer source memory for answers retrieved from a smartphone than for answers they initially attempted to retrieve from memory. Experiment 2 demonstrated that memory for the information was equivalent across conditions. These results demonstrate that we are prone to confusing information retrieved from internal and external memory stores, and we have a cognitive bias to appropriate external knowledge as our own.