Significant improvements in door-to-balloon times have led to a reduction in mortality in ST-segment elevation myocardial infarction; however, mean symptom-to-door times remain at 2 to 3 hours. An intracardiac electrogram monitoring device may be beneficial in high-risk patients by alerting them to rapidly progressive ST-segment changes indicative of acute coronary occlusion. The Cardiosaver and DETECT phase I clinical studies demonstrated the safety, feasibility, and potential benefit of using an intracardiac electrogram monitoring device to alert the patient to seek medical attention. The goal of the randomized, prospective ALERTS Trial (Clinicaltrials.gov no. NCT00781118) is to evaluate the efficacy of an implantable monitoring device (IMD) in reducing the composite of either cardiac or unexplained death, new Q-wave myocardial infarction, or symptom-to-door time of >2 hours for confirmed thrombotic events. The IMD alerts the patient in real time when ST-segment deviation from a personalized baseline exceeds the trigger threshold. The trial is designed to enroll high-risk post‐acute coronary syndrome patients or patients with previous multivessel coronary artery bypass surgery. All patients have the IMD implanted, with 1:1 unblinded randomization to the alerting feature being either turned on versus turned off for the first 6 months. Randomization occurs at the first follow-up visit, 7 to 14 days after the implantation of the IMD. Subjects then return for follow-up visits at months 1, 3, and 6 and thereafter every 6 months until closure of the investigational device exemption. Subjects who cannot be implanted successfully or who have the device explanted are removed from the study and followed up for a minimum of 30 days post‐procedure. If a subject experiences a device-related complication and/or adverse experience, the subject is followed up until resolution or until the condition becomes stable and no further change is anticipated.