Smartphones are the most personal devices. The kind of apps we install are therefore closely linked to our habits and personality. In this research-in-progress paper, we aim to provide two key contributions. First, we aim to advance the body of knowledge in technology adoption research by explaining adoption of specific mobile apps by using the Big Five personality traits. Second, we provide a scalable method of deriving personality traits based on easily accessible data. We show that it is possible to determine a user's personality in reasonable accuracy by evaluating her history of app installations and update events.