## 3 Future Perspectives of Wearable Devices during Pandemics
For example, sedentary individuals should receive a warning via wearable devices when the daily step count decreases by 1000 steps compared with the average number of steps at baseline. If the daily step count is decreased by 4000 steps or more, healthcare professionals should directly contact such individuals and check their health status. There are different types of intervention methods to promote physical activity (e.g., in-person, telephone, emails, text messaging, mobile applications, and social media), and among them, the smartphone-based intervention effectively improves total physical activity and daily steps in children and adolescents [39]. In addition, wearable activity trackers are recognized as useful and acceptable healthcare devices in individuals aged >50 years and with chronic disease [40]. Given that 66.9% of the world's population have mobile phones [41], the intervention via smartphone applications is the most promising method. Previous studies showed that the use of technologies such as smartphone applications and social media improves obesity, glycemic control, eating habits, and daily physical activity in patients with diabetes [42]. [PERSON] et al. [5] proposed practical application scenarios of wearable devices with telehealth systems during pandemics. The scenarios are composed of hospital and outside hospital scenarios that involve various facilities and resources such as nursing homes, community care organizations, COVID-19 testing centers, mobile hospitals, hospitals and healthcare workers who monitor patients' condition in real-time, home monitoring systems, health checking centers, public areas, and COVID-19 contact tracing systems. The close network centered on a cyber hospital (database) is build up in the scenarios, and wearable devices play a vital role in data exchange between a cyber hospital and each facility or individual. Wearable activity trackers such as smartwatches are the keys to successful communication between individuals and a cyber hospital. To establish an effective healthcare system for pandemics based on the scenarios, it is significant to increase the prevalence and use rate of wearable devices among the general population. In a community-based cohort, the ownership and use rate of wearable activity trackers was only 19.6% [43]; thus, some public awareness activities and policies for the popularization of wearable technologies encouraging the application of wearable activity trackers in clinical practice may be needed. In addition, there are barriers to the purchase and use of wearable activity trackers such as cost and motivation. [PERSON] et al. [44] indicate that a free wearable activity tracker can facilitate behavior change to be more physically active in older adults with chronic diseases, while continued training and support are needed. A systematic review reported that the evidence on the effect of economic instruments including fiscal government policies to promote physical activity behavior change is limited [45]; however, government support is essential for the spread of wearable activity trackers and promoting physical activity. For instance, European governments distributed smartphone contact tracing applications for free to slow the spread of the COVID-19 pandemic [46]. It is desirable that governments are responsible for the spread of wearable devices in preparation for future pandemics. On the other hand, the validity and reliability of consumer-wearable activity trackers have been already assessed, and there was a high (Pearson or intraclass correlation coefficients \(\geq\) 0.8) validity of steps and a high inter-device reliability for steps, while sleep and energy expenditure were not measured adequately using existing wearable activity trackers [31]. However, technological improvement and innovation will advance, and the use of wearable activity trackers in daily clinical practice will become increasingly significant.