Since their inception, wearable devices have primarily focused on monitoring external user behavior and activity levels. However, recent breakthroughs in functional materials, electronics, and advanced algorithms are expanding the data landscape. Today, we can collect an ever-increasing number of data points continuously and unobtrusively. This abundance of information offers a transformative opportunity for deeper contextual understanding, moving beyond simple behavior tracking to objective assessments of a user's mental and physiological status. In this contribution, we review recent advancements in the field, with a specific focus on how sensor fusion and seamless access to biosignals such as EEG and EMG are reshaping the next generation of wearable devices.
