In many human-machine interaction applications, user's emotion can be recognized to reveal the additional user's information which can improve the system's response and make the system to be more user-friendly. Detecting the ”paralinguistic events” is a way to classify the user's emotion state. One of the most obvious ”paralinguistic events” is laughter. The paper provides a brief review focusing on the studies of automatic laughter detection technology. The topics about the acoustic properties of laughter, the famous experimental database, extracted features and the laughter classifiers are discussed. We expect the laughter detection technology can be applied in many application scenarios that provide more interesting human-machine interaction mechanism.