Affected by the Covid-19 pandemic, the way adolescents receive their education has changed drastically from offline classrooms to online digital space. Despite the benefits of digital devices, we must also be cautious of the possible negative impacts of using digital devices excessively. In this study, we proposed a smart planning course to support adolescents in managing daily digital device usage. Meanwhile, we examined the effects of this course through a novel multimodal learning analytics (MMLA) approach. Although results of the quasi-experiment indicated few significant effects of the intervention, possibly due to its timing, the proposed MMLA approach was shown to provide more comprehensive and refined data compared to traditional methods. Future studies can use this approach for further activity-based analysis of students' digital well-being.