The widespread use of mobile and smart technical devices allows a multi-faceted approach to research into the dynamics and maintenance of mental stress. Particularly interesting relationships can be identified when objective behavioral data (e.g., how deep did I sleep? How many steps did I take?) can be related to a person's subjective experience. The best way to achieve this goal is to combine objective behavioural data with classical questionnaire data. In the BluesWatch study, in cooperation with technology provider thryve, it will be examined how well Smartwatches can be used to investigate these relationships in clinical research. It will also be examined whether findings from previous research can be replicated and explored how Smartwatch data can be used to predict treatment success in Internet-based interventions.