Technological developments and advancements are imminent, where the human user remains in the center as the end consumer. Hence, having a better understating of natural human reactions (both in the behavioral and emotional levels) cannot be avoided to better suit such a solution. With recent developments in the fields of vision, voice, and sentiment analysis, some external self-expressions can be captured and evaluated through means of edge device computing (e.g. smartphones). However, "faking" is a commonality amongst most users, and external expressions do not necessarily match the true physiological state of the person. Hence, Letos offers a complementary sensor solution that can evaluate true spontaneous physiological reactions as they occur in our utmost natural surroundings – at home, at the office, or when we commute on the road.