## 1 Introduction  
Many elderly people require regular assistance for their daily living and healthcare. There is an increased awareness in developing and implementing efficient and cost-effective strategies and systems, to provide affordable healthcare and monitoring services particularly aimed at the aging population. Aging in place is the ability to live in one's own home and community safely, independently, and comfortably, regardless of age, income, or ability level. For elderly people, moving in with the family or entering a nursing home or assisted living facility could be cause of psychological stress, which can lead to health issues and lowering their quality of life. Allowing elderly people to maintain their quality of life as they get older and as long as possible in their homes is important both for the person as well as for the sustainability of public healthcare systems. According to the \"World Population Prospects 2019: Highlights\" of the United Nations [1], in 2018, for the first time in human history, people aged 65 years or over outnumbered children under five years of age worldwide. The projections indicate that in 2050 there will be more than twice as many older people as children under five (see Figure 1). Among the aging countries there is Italy. As for 2016, Italy has 22.1% of residents aged more than 65, and 6.7% aged more than 80 years. These percentages are expected to increase up to 33% and 15% respectively within 2070 [2]. With these numbers, Italy has one of the oldest population in Europe (see Figure 2 left) and one of the countries affected by the highest _old age dependency ratio_, i.e., the ratio of people older than 64 compared with those aged 15-64 (see Figure 2 right). If the aging trend is confirmed, there will be fewer people to take care of the elderly in the distant future. It is not surprising that within the \"Horizon 2020\" Research and Innovation Program of the European Union, many national projects in Italy are oriented toward the older population to promote healthy and active aging, and test new technologies for the sustainability of the healthcare system. The final aim of most of these projects is to develop a novel assistance system with the goal of preserving as long as possible the remaining autonomy of elderly people so that they can live at home instead of being transferred to public or private nursing homes [4]. Always under the \"Horizon 2020\" umbrella, a noteworthy program called Active and Assisted Living (AAL) [5] stands out. It is a funding program that aims to create a better quality of life for older people and it is placed in the field of healthy aging technology and innovation. Assisted living technologies can be of great importance to take care of elderly people and help them to live independently. One way to achieve this is to monitor the activities of the elderly in a continuous fashion to detect emergency situations as soon as possible. For example, using ambient or wearable sensors it could be possible to analyze the daily activity of the person and detect if any activity  
Figure 1: People aged 65+ years old make up the fastest-growing age group worldwide. Data from [3]. Figure 2: Estimated aging trend in Italy as per the Italian National Institute of Statistics (ISTAT). Estimates are shown within 90% confidence intervals. is outside normal activity patterns. Also, it could be possible to prevent health issue by monitoring the person's behavior with respect to dehydration and lack of food intakes. Finally, emergency events such as falls and pains could be signaled to the healthcare facilities or family members for immediate intervention. These events can be automatically registered by the sensors or signaled by the person requesting help. Figure 3 shows a general architecture of an Ambient Assisted Living (AAL) system that can be used for monitoring elderly people.