This paper discuss the ability to obtain a reliable pervasive information at home from a network of localizing sensors allowing to follow the different locations at which a dependent (elderly or handicapped) person can be detected. The data recorded can be treated as the sequence of color coding numbers of balls (symbolizing activity-stations) taken in a Polya’s urn, in which the persistence of the presence in an activitystation is taken into account by adding a number of balls of the same color as the ball just drawn. We discuss the pertinency of such a procedure to early detect sudden or chronic changes in the parameters values of the random process made of the succession of ball numbers and we use it to trigger alarms.