Background: Many suicide risk factors have been identified, but traditional clinical methods do not allow the accurate prediction of suicide behaviors. To face this challenge, we developed emma, an app for Ecological Momentary Assessment/Intervention (EMA/EMI) and prediction of suicide risk in high risk patients. Objective: We wanted to test the feasibility of implementing this mHealth-based suicide risk assessment and prevention tool and its impact in subjects at high risk of suicide in real world conditions. Methods: The EMMA Study is an ongoing longitudinal interventional multicenter trial in which patients at high-risk for suicide (n=100) use emma for 6 months. During this period, they complete four EMA types (daily, weekly, monthly, spontaneous) and may use EMI modules. Participants undergo clinical assessment at month 0, 1, 3 and 6 after inclusion. Results: Among the 43 patients already recruited in the EMMA Study, 14 participants had completed the follow-up. Their data were analyzed to evaluate emma implementation and impact on suicide risk management. EMA completion rates were extremely heterogeneous among the 14 participants with a sharp decrease over time. The completion rates of the weekly EMA (25% to 87.5%) were higher than for the daily EMA (0% to 53.3%). Most patients (n=10/14) answered the EMA questionnaires spontaneously. Similarly, the Safety Plan Modules use was very heterogeneous (2 to 75 times). Specifically, 11 patients used the Call Module (1 to 29 times), designed by our team to help them to get in touch with healthcare professionals and/or relatives during a crisis. All patients used the Breathing Space Module and 8 the Emotion Regulation Module (1 to 46 times). The diversity of patient profiles and use of the EMA and EMI modules proposed by emma was highlighted by three case reports. Conclusions: These preliminary results suggest that it is possible and acceptable to collect longitudinal fine-grained contextualized data (EMA) and to offer personalized intervention (EMI) in real time to people at high risk of suicide. Patients have different clinical and digital profiles and needs that require a highly scalable, interactive and customizable app. To become a complementary tool for suicide prevention, emma should be integrated in the existing emergency procedures.