levels of light of an area when the person is in that area, evaluated and stored every hour; 4. *hearing*, initially evaluated through specific tests; indicators are the response time to a ringing bell, evaluated and stored periodically as a result of a test performed under specific conditions; 5. *cognition*, evaluated by means of the Mini Mental (Folstein et al. 1975) and Clock Drawing (Yamamoto et al. 2004) tests; indicators are represented by test results; 6. *insomnia*, initially evaluated by means of a questionnaire; the indicator is the quality of sleep in three different moments of the sleeping period: start of the sleeping period, heart of the night, early morning; 7. *emotional stability*, initially evaluated by means of the GDS test (Yesavage et al. 1983); the indicator is a computer-aided version of the GDS test.

ADLs For items in this class, we are interested in the estimated level of dependency in performing the Activities of Daily Living (ADLs) mentioned in the Katz scale (Katz et al. 1970), in particular:
1. *mobility* initially evaluated through the PASE scale; indicators are the walking speed, the number of steps and the average daily walking time; 2. *dress* evaluated according to specific tests performed by caregivers; 3. eat evaluated by means of the Mini Nutritional Assessment Test (Guigoz et al. 1994);
4. bathing has no indicators in the current version; 5. toileting has no indicators in the current version.

We want to point out that reasoning with ADLs is not aimed at activity recognition as in other approaches to monitoring (Pollack 2005). We start from absolute evaluations as input and then concentrate on possible inter-dependencies that may influence the level of autonomy with which a person performs an ADL,
thus predicting a risky evolution of the health state according to correlations with other items as detailed in Section 4. We believe that the analysis of such dependencies is crucial for prevention.

Instrumental Activities of Daily Living (IADL) from the Lawton scale (Lawton 1988) have not been included either, except for drugs intake and use of the telephone. This choice has been guided by the fact that they have a lower impact on other health-related items and the evaluation is too complex to be performed in a non intrusive way.

Risk Assessment The risks we consider in the SINDI system are represented by the potentially most dangerous situations for elderly people at home, namely:
1. *falls*, the risk is initially evaluated according to the Tinetti POMA scale; it can be influenced by specific pathologies and drug intake used as indicators; 2. *depression*, the risk is initially evaluated according to the GDS scale (Yesavage et al. 1983); it can be influenced by specific pathologies and drug intake used as indicators;