# A Review of Blockchain Technology Applications in Ambient Assisted Living
## 1 Introduction  
Ambient assisted living (AAL) is a research field that aims to bring smartness to our everyday environments by acquiring data from various sensors, understanding people's activities, behavior, and living problems, and deciding on proactive interventions to support the management of identified issues (see Figure 1) [1]. With the advance in sensing technologies and the prevalence of miniaturized, affordable Internet of Things (IoT) sensor applications have been developed to improve the beneficiary's quality of life and support personalized care [2]. A wider range of proof of concept applications for various use scenarios along with associated technologies can be found in the literature, such as fall detection systems [3], cognitive decline management [4], personalized care [5], remote follow-up [6], nutrition management [7], medication review [8] and well-being management [9]. Having more IoT devices and sensors associated with living environments leads to collecting patient data that must be shared among multiple parties on different sides [10]: validators, processors, healthcare stakeholders, etc. Nowadays, the ambient assisted living systems move the data collected in cloud systems (see Figure 1), where the potentially unlimited computation resources help in dealing with analytics and decision making [11]. Using decentralized distributed ledger solutions will allow multiple nodes to host the same set of encrypted data in multiple care systems that are hosted in different places and kept up to date with the actual state and data of the system [12]. Additionally, most of the collected data are rather sensitive and personal data of vulnerable people; thus, security and privacy have always been issues to deal with [13]. They constitute a barrier between vulnerable people and assistive technologies and prevent the adoption and good use of existing software solutions in the field [14]. People may become digitally vulnerable as data theft, fraud, and the unauthorized use of personal, medical, and financial information are often not even known by the victims [15]. The privacy and security problems are critical for data-driven assisted living applications and IoT networks such as the Internet of Medical Things [14]. Data ownership and elimination of potential breaches are objectives for keeping the data, and the system secured [16]. However, because of the lack of precise specifications, even ordinary procedures might result in security breaches [17]. There is a strong need to make such applications transparent, immutable, and distributed [18]. In general, in the discussions concerning privacy and security, how consumers understand privacy is key [19]. People are more inclined to value decentralized solutions for their capacity to safeguard their privacy goals [20]. On top of technical privacy issues, lately, personal details (i.e., used to identify a person) have become one of the most valuable commodities [21]. This information might be as basic as a name or identification number, or it can be more sensitive, such as medical or behavioral data [22]. As the world becomes more digitized, internet activity is increasingly recorded, often without the user's knowledge or agreement, constituting a barrier to ambient technologies adoption. Blockchain technology is seen as a good solution for tackling IoT monitoring, data management, interventions, and privacy concerns [23] in ambient assisted living applications [24]. Stakeholders from the ambient assisted and care fields are interested in integrating blockchain technologies into their systems to benefit from improved security, privacy, and data ownership (see Figure 2) [24]. Conventional ambient assisted living solutions use centralized cloud-based models focused on structuring data rather than privacy, ownership, and decentralization. The adoption of blockchain technology can change this landscape [25].