A single elderly, dependent subject was monitored for a period of three months. Data were collected from 12 sensors in his apartment. We investigated new criteria for diagnosing abnormal events with more reliability. Initial results suggested that six diagnostic functions could be achieved using only presence sensors. These were: immobility detection; the level of agitation; the speed of motion in chosen areas; the distance covered; the time spent in given areas of the apartment; and the activities of getting up, going to bed and going to the toilet. The analysis was based on calculation of thresholds from past behaviour of the user for automatically defined temporal bands. Any variation in these criteria may represent a change in the subject's physical abilities and may thus allow the remote identification of potential risk.