Background: Mobile health innovations are well adapted for ambulatory coronavirus disease 2019 (COVID-19) patients who risk clinical deterioration at home during the second week of illness. Methods: A short message service (SMS) communication program was implemented by French physicians to monitor COVID-19 patients after discharge from outpatient or emergency care. The aim of the SMS tracking is to advise patients about their need for medical reassessment if reporting worsening of COVID-19 symptoms. A follow-up via SMS to all confirmed positive patients in the Nîmes area (France) was established. Every morning, patients received four follow-up questions. Daily responses were converted to green, orange or red trees, analysed in real time by physicians. "Red" patients were called immediately to check their condition and organise transfer to hospital if needed. "Orange" patients were called within two hours to verify whether the specific instructions following the SMS had been followed. Results: From March 21 to June 30, 2020, 1007 patients agreed to sign up to the SMS tracking, 62% were women and the mean age was 41.5 years (standard deviation (SD) 16.0). During follow-up, 649 (64%) became "orange" and 69 (7%) "red". Ten patients were directly admitted to the Infectious Diseases Department during their follow-up due to clinical worsening, all but one as a result of SMS alerts and subsequent telephone assessment by physicians. Conclusion: SMS tracking platforms could be useful as an early warning system to refer patients with worsening clinical status to hospital-based care or additional clinician advice.