Psychiatric evaluations of patients' diagnoses and symptoms largely rely on their autobiographical memory, ability to reflect and verbalise their inner experience and behaviour, and the interviewers' ability to conceptualise these communications. Reliable biomarkers for purposes of diagnosis and follow-up of illness course and treatment effectiveness are constantly sought. Both clinical experience and longitudinal research on mood variability among patients with mood disorders indicate a need for improved methods for patient monitoring. Pioneering online mood charting tools1 have existed for over a decade. Accumulating studies have already demonstrated that smartphone data can serve as an electronic biomarker of illness activity in bipolar disorder (BD). To read the full article, log in using your NHS OpenAthens details.