There is a growing focus on monitoring health in uncontrolled (aka in-the-wild) settings. This is partially due to the limitations of occasional formal assessments, and to the increasing availability of off-the-shelf sensing devices and applications. This change of paradigm promises fine-grained monitoring of chronic and neurodegenerative diseases, early prediction of health conditions, accessible self-management, and the enablement of more effective personalised interventions. Recent research shows us the potential of these ubiquitous technologies: with body-worn accelerometer sensors, it is possible to monitor disease fluctuations in free-living environments; predict hospital readmission; monitor depression via social media posts; detect continuous exposure to stress with wrist-worn devices; use smartphones to passively monitor diseases or perform rapid tests in low-resource settings; among many others.