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Changes in the behavioral activity of elderly people living alone at home may be an indicator of their functional health status. In this paper, we evaluate the characteristics of a pyro-electric infrared detector (PIRD) and demonstrate that the sensitivity of the detector can be increased if four sensors, one at each corner of the room, is installed (instead of one). The experimental results suggest that the spatial sensitivity of the PIRD is non-uniform at different distances for different walking speeds. If a detector is used in a room of dimension half the maximum detection range of the PIRD, there exist dead points where detection sensitivity is very low, giving rise to false alarms. Hence, a single detector installed in a room fails to respond to small movements (hand movements etc.) in the extended range. Four detectors at each corner of the room helps to increase the sensitivity of the detection whereby even small movements such as reading a book, telephonic conversation etc. can be identified.