In many of countries facing the aged society, it is expected that the serious society problem like lonely death will be increasing. Therefore, the system watching over elder's life is very important. Then, we developed the system that watching over elder's life using information about indoor ambient atmosphere changes. Indoor ambient atmosphere is changed by acted daily activities regardless of the age or sex of resident. Our system acquired such changes using 7 sensors (gas, temperature, humidity, brightness) and could recognize daily activities using information that extracted by observer. In this paper, we describe a method for detection of the information that related resident's daily activities automatically. For such purpose, we propose a method for threshold setting using statistically technique and a method for extraction of information related resident's daily activity using multiple sensors.