Georgios Papastefanou gave us an overview of the emotions and sensations that can be measured through a device. Tiredness is measured as a decrease in sympathetic nervous system activation. Fear also has very distinct physical markers.
Happiness is more difficult to quantify. There’s also a difference between the self-reported emotions of young men vs what their physiological data indicates. There’s a greater correlation between the self-report and data in women.
Just using the tracking devices has changed behavior for Georgios himself. His suggestion is to give a mobile measurement device to someone who is dealing with obesity and ask them to mark their feelings of hunger. If someone is more aware of how hungry they are feeling, they get a good feedback loop of when they are eating due to hunger pangs vs. other reasons they have for eating.