Learners use digital media during learning for a variety of reasons. Sometimes media use can be considered "on-task," e.g., to perform research or to collaborate with peers. In other cases, media use is "off-task," meaning that learners use content unrelated to their current learning task. Given the well-known problems with self-reported data (incomplete memory, distorted perceptions, subjective attributions), exploring on-task and off-task usage of digital media in learning scenarios requires logging activity on digital devices. However, we argue that logging on- and off-task behaviour has challenges that are rarely addressed. First, logging must be active only during learning. Second, logging represents a potential invasion of privacy. Third, logging must incorporate multiple devices simultaneously to take the reality of media multitasking into account. Fourth, logging alone is insufficient to reveal what prompted learners to switch to a different digital activity. To address these issues, we present a contextually activated logging system that allows users to inspect and annotate the observed activities after a learning session. Data from a formative study show that our system works as intended, and furthermore supports our assumptions about the diverse intentions of media use in learning. We discuss the implications for learning analytic.