With increase in the population of elderly people in Japan, the annual number of solitary deaths is increasing. Hence, prevention of solitary death is becoming an urgent task nowadays. This paper presents a system for monitoring usual behaviors in elderly people, that can be used as crime-prevention and a health control system. The proposed system uses odor sensors which can hardly invade privacy. In a previous system behaviors of a solitary elderly are recognized by placing odor sensors on the surface of a room and measuring levels of air pollution. However, since some materials are heavier and lighter than the air in polluted air, the system could not get information from upper air. For this reason, in this study we measure levels of air pollution by changing the height of odor sensors. The major achievement of this study is to realize various usual situations of elderly people and to reveal that the level of air pollutions can be distinguished into three layers. Moreover, our proposed system could detect entering and leaving of a person by analyzing measured data obtained from odor sensors placed at several heights.