Researchers attempting to survey refugees over time face methodological issues because of the transient nature of the target population. In this article, we examine whether applying smartphone technology could alleviate these issues. We interviewed 529 refugees and afterward invited them to four follow-up mobile web surveys and to install a research app for passive mobile data collection. Our main findings are as follows: First, participation in mobile web surveys declines rapidly and is rather selective with significant coverage and nonresponse biases. Second, we do not find any factor predicting types of smartphone ownership, and only low reading proficiency is significantly correlated with app nonparticipation. However, obtaining sufficiently large samples is challenging—only 5 percent of the eligible refugees installed our app. Third, offering a 30 Euro incentive leads to a statistically insignificant increase in participation in passive mobile data collection.