The system according to the invention interprets sensor observations by tracking objects and by collecting information about the objects by means of the tracking and by using this information for affirming events linked to the objects and in producing information describing the events. The system detects events according the conditions defined for them, on the basis of sensor observations. The conditions can relate to the essence of the objects, e.g. to the strength of the observations linked to the object, to the size and/or shape of the object, to a temporal change of essence and to movement. The event conditions used by the system can comprise conditions applying to the location of the object. The system according to the invention can be used e.g. for detecting the falling, the getting out of bed, the arrival in a space or the exit from it of a person by tracking an object with a dense sensor field, and for producing event information about the treatment or safety of the person for delivering to the person providing care.