It is very difficult to judge when a person is happy. The current way of estimating is to take a survey. However, surveys are prone to failure and they are not very exciting for the surveyors. The people surveyed make a best guess of questions, based on recall.
One of the toughest surveys is to find out the happiness of any person. Typically, these were done by asking in a survey but a group from Princeton has used mobile phones to conduct instantaneous surveys. Find out more at the link below but doing more of the surveys online can help get quick responses but also get a more true response since the response was collected when the feeling was real.