# A Scalable Solution to Detect Behavior Changes of Elderly People Living Alone
## 1 Introduction  
The world population is ageing rapidly. People aged 65 years or older are now the fastest growing age group, and some projections [1] indicate that, in 2050, the number of persons aged 65 and over will surpass two billion (16% of the world's population, up from 9% in 2019). In the same time horizon, the number of persons aged 80 years or over is expected to triple (426 million in 2050, up from 143 million in 2019). As old age comes with a variety of health issues (cardiovascular diseases, dementia, frailty, and many others) this demographic shift is likely to increase the need of medical services beyond the limits of the medical systems of almost any country. Most elderly prefer to age in place [2], i.e., to spend their last years in their own homes retaining a certain level of independence, rather than go to nursing homes, or other residential care centers. This proved to be the right option, as a large share of the total COVID-19 deaths occurred in nursing homes (as much as 40% in New York City [3]). On the other hand, the exponential advances witnessed in the past decades in all technological fields fueled the hope that new assistive technologies will lead to the development of effective solutions to help elderly people live independently in their homes. The term assistive technology designates  
_\"any device or system that allows individuals to perform tasks they would otherwise be unable to do or increases the ease and safety with which tasks can be performed\"_. [4]  
The simplest setup that allows the patients to receive medical consultations using standard videoconference equipment, remote monitoring of certain medical devices (e.g.,pacemakers, implantable loop recorders, etc. ), and other medical services without the need to go to a medical clinic is telemedicine (see Ref. [5] for a discussion on the formal definitions of telemedicine and related terms telehealth and telecare). This setup allows the medical staff to increase the number of patients served, and the patients to access with ease the services of multiple medical specialists directly from home. On another level of complexity of the assistive technology, when \"a home or dwelling [is equipped] with a set of networked sensors and devices that extend the functionality of the home by adding [artificial] intelligence, automation, control, contextual awareness, adaptability, and functionality both remotely and locally, in the pursuit of improving the health and wellbeing of its occupants and assisting in the delivery of healthcare services\" [6], it is called a smart home. We should note that the definition of smart home cited above (from Ref. [6]) is not complete. Some smart homes are designed for optimizing the energy consumption (as in Ref. [7]), while others are designed with a focus on environmental sustainability [8]. Comprehensive reviews of the literature on smart homes and their applications are available in Refs. [9; 10; 11]. The concept of Ambient Assisted Living (AAL) is wider than that of smart home at least from the perspective of the place where the assistance occurs: while in smart homes the assistive technology is specific for indoor use and its deployment is limited to the residential space, AAL applications go beyond the home or dwelling of the users and seek to provide assistance and monitoring also in public spaces, shopping centers, public transportation, in the work environments, and in outdoor spaces (see Refs. [12; 13] for a review of the state of the art in AAL). In what concerns the specific functions and actions of the assistive technology, [PERSON] & Hensel in Ref. [14] identified the following categories:  
* Physiological monitoring, by collecting and analyzing data about certain physiological parameters like pulse rate, blood pressure, respiration, level of oxygen in the bloodstream, temperature, blood sugar level, etc. This type of application typically relies on wearable or implantable sensors (see Refs. [15; 16]).