Because of the frequent asymptomatic presentation of atrial fibrillation (AF), stroke is too often its first manifestation. 1 For effective stroke prevention, timely diagnosis of AF is crucial. Mobile devices are becoming ubiquitous, providing significant possibilities for screening applications. In mechanocardiography, mechanical cardiac activity is recorded with accelerometers and gyroscopes, standard components of modern smartphones. 2 In our previous proof-of-concept study, smartphone mechanocardiography demonstrated 94% sensitivity and 100% specificity for detecting AF among 39 subjects. 2 Here, we validate smartphone mechanocardiography detection of AF against visual interpretation of telemetry electrocardiographic recordings in hospitalized patients.