In recent years, the use of smartphones has increased exponentially, and so have their capabilities. Together with an increase in processing power, smartphones are now equipped with a variety of sensors and provide an extensive set of API. These capabilities allow us to extract data related to environment, user habits, and operating system itself. This data is extremely valuable in many research fields such as user authentication, intrusion, and information leaks detection. For these reasons, researchers need a solid and reliable logging tool to collect data from mobile devices. In this paper, we first survey the existing logging tools available on the Android platform, comparing their features and their impact on the system. Then, we present DELTA - Data Extraction and Logging Tool for Android, which improves the existing Android logging solutions in terms of flexibility, fine-grained tuning capabilities, extensibility, and available set of logging features. We fully implement DELTA and we run a thorough performance evaluation. The results show that our tool has a low impact on the performance of the system, on battery consumption, and on user experience. Finally, we make the DELTA source code available to the research community.