## 3 Results
### Common Themes for RQ2  
RQ2: To what extent are remotely monitored sounds and vibrations used simultaneously in assisted living or smart homes? 3.1 Theme 1: The Extent of Simultaneous or Independent Remote Monitoring of Sounds and Vibrations Other Than for Detecting Falls  
There is limited evidence that acoustic and vibration technologies have been used simultaneously for remote monitoring. Only two studies tried to monitor remotely using sounds and vibrations simultaneously, and both studies originated from the same authors [50; 51]. Six articles adopted acoustic technologies only [46; 47; 48; 49; 50; 51; 54], whereas four adopted vibration technologies only [47; 55; 56; 57]. Of the two articles that involved using both acoustic and vibration technologies, one was a conference paper [52], representing work-in-progress prior to the publication of the other [53]. Together with the observation that other articles reviewed tried either acoustic or vibration technologies alone, the results showed limited attempts to apply both technologies simultaneously. Also, no attempt has been made to correlate airborne and structure-borne signals and, thereby, to discriminate between the sources based on any such correlation. The two studies that used sounds and vibrations simultaneously were focused on detecting falls [52; 53]. The system comprised an accelerometer and a microphone to detect floor-borne and air-borne signals from a fall and to differentiate these signals from other sounds and vibrations around a home to enhance the reliability of remote monitoring in a residential environment. However, the combined system was not tested with applications other than falls, so its potential usefulness in this respect has not been explored. Although the variety of applications for vibration technologies was wider, the majority primarily focused on detecting falls. One study showed an attempt to detect and  
Figure 3: A summary of common themes for RQ1. differentiate human activity patterns in general [47]. However, the other four articles were all related to identifying fall patterns [55; 56; 57]. The variety of applications for acoustic technologies was wider than for either vibration alone or combined use. Only one out of five studies focused on detecting falls [48]. One study attempted to follow a similar line. However, it started with a qualitative interview that related most to the habitual living patterns of older adults in a care home, then gathered relevant acoustic information and trained artificial intelligence to recognise human activity indoors [49]. Another one attempted to identify patterns to recognise events using machine learning based on acoustic and other low-level sensory data (light, humidity, temperature) [46]. The remaining studies approached detection in a similar manner to the above. However, they utilised only acoustic data in an indoor environment and then employed a machine-learning approach to training the recognition and differentiation of human activities [50; 51; 54]. While vibration monitoring focused more on detecting vibration, acoustic technologies appeared to have a broader application, although they emphasised the development of machine learning algorithms rather than hardware. 3.2. Thememe 2: Principles, Availability of Technologies, and the Associated Advantages and Disadvantages  
The two studies, which simultaneously adopted vibration and acoustic technologies, used an accelerometer and microphone as the sensors [52; 53]. For studies involving only vibration technologies, three studies utilised accelerometers [45; 53; 54], and one utilised a radar system coupled with Doppler sensors. However, in both systems, the sensors were floor-based [57]. Studies involving acoustic technologies used microphones [5; 46; 48; 49; 50; 51]. The review section of these articles mentioned the range of technologies used to monitor older adults' conditions remotely and their respective advantages and disadvantages.