Abstract: The invention relates to a device for detecting atrial fibrillation of a subject, comprising a member comprising —mechanical connection means to wearably connect the member to a subject; —the member further comprising an optical sensor arranged to measure a signal representing a blood perfusion parameter of the subject; the member comprising the optical sensor and mechanical connection means at such relative positions that when the mechanical connection means connect the member to the subject, the optica! sensor operatively faces the subject. The device is arranged to detect atrial fibrillation of the subject based on the signal measured by the optical sensor.