John is a 35-year-old software engineer, married, and with one child. Prior to the COVID-19 pandemic, he was engaged in daily physical activities, regularly communicated with friends and family, slept well, and rarely had problems associated with stress. However, with the worsening of the global health crisis and the need for restrictive actions, John faced difficulties maintaining his healthy habits and gradually began to have problems with sleep, loneliness, and stress. If a questionnaire were applied to assess John's Quality of Life in 2019, the physical and psychological domains scores would likely be high. Nevertheless, the reapplication of this instrument in 2021 would bring different results.

While in 2019, the scores were good, in 2021, they indicated an alert situation. Keeping these indicators at low levels can lead to severe health problems such as depression and chronic anxiety. The ideal scenario would be to continuously monitor these health indicators to alert John as soon as possible about the worsening in his indicators. However, the continuous application of self-reported questionnaires (an intrusive and non-transparent kind of monitoring) makes it challenging to engage the participants.

This illustrative scenario can also be analyzed considering the perspective of public and private health managers. The growing demand for health services has forced searching for methods to optimize resources, promoting better healthcare services. John's worsening health is likely to impact his use of health services. Thus, continuous monitoring of this situation could trigger early alerts to anticipate interventions, such as promoting preventive care in a personalized way. This context reinforces the need for services that non-intrusively monitor people's QoL, seeking to anticipate situations that tend to worsen with unhealthy habits.