## 1 Introduction  
The global population is ageing, and that in the United Kingdom is no exception since older adults aged 65 or older represent 18.2% of the population. This proportion is expected to increase to 24% by 2037 [1]. However, longer life expectancy does not necessarily translate into better health. For some, ageing may be associated with a higher incidence of disability, chronic diseases, and other conditions, which increases pressure on the health and social care systems [2]. Approximately 70% of older adults require total assistance for activities in daily living [3], and 35% require some support to manage their everyday lives, typically from family members and friends [4]. There are associated costs. For example, the costs of unpaid care for people with Alzheimer's or other dementia diseases provided by family members or relatives amounted to about $233.9 billion in the US [5]. Moreover, caring for older adults with chronic illness or deteriorating physical and mental health, making them less autonomous, can compromise caregivers' physical, mental, social, and economic status [6, 7]. However, emerging assistive technologies help to maintain and enhance the physical and cognitive functions and well-being of vulnerable groupschallenged by daily living tasks. They enable older adults to age well, for example, by enabling them to maintain their participation and engagement in activities domestically and in community settings. Also, they improve the cost-effectiveness and quality of health and social services [8]. There is a lack of consensus on the definition of assistive technologies [9]. However, generally, they refer to information and communication technologies (ICT), stand-alone assistive devices, and smart home technologies developed to help older adults age in place safely, actively, and autonomously in the familiar environment of their homes [10; 11]. The benefits of assistive technologies include decreasing the risk of falls and other accidents [12], improving inhibition and working memory [13], increased physical activity and reported quality-of-life scores [14], an enhanced sense of safety and security [15; 16], augmented health monitoring and management [15; 16], and better assisted daily life functioning [17]. Remote sensing technologies, a class of assistive technologies, are increasingly being used to deliver such benefits to older adults. These include wearable inertial sensors in smartphones for detecting falls [18], active infrared-based sensors for monitoring indoor wandering behaviour [19], and a combination of motion, light, and temperature sensors to maintain safety in daily activities [20]. As well as being used in the domestic setting, assistive technologies have been applied in institutional settings to inform carers when appropriate actions are required, thereby partly alleviating their burden of caring [21]. Remote sensing technologies have received growing attention given their potential to identify hazardous activities and monitor health conditions and safety in a wide range of living environments, such as sheltered housing, extra-care housing, and care homes [21]. Among the technologies available for health and well-being surveillance, ambient sensing technologies have received less attention than wearable sensors. The detection of environmental signals can be mechanical (e.g., vibrations via accelerometers, motion via gyroscopes), optical (e.g., fibre-optic detection or cameras), or electronic (e.g., semiconductor temperature sensors). Ambient sensing is preferable to wearable sensors since it is less intrusive. Moreover, ambient sensors do not need charging, operate twenty-four-seven, and do not cause discomfort from being carried [22], which is a major disadvantage of wearables. Also, they eliminate the risk associated with wearing devices in high-risk areas, such as bathrooms [23]. In addition, they enable monitoring even when the user forgets to carry or charge the wearable device.