An opto-electronic device (S) for detecting the movement of yarn (Y) (10) passing transversely through a detection zone (11) on the storage drum (3) of a yarn feeder (F), has at least one light source (L) directed on the detection zone (11), at least one reflector (B) fitted on the storage drum (3) a short distance away on the side of the detection zone (11) away from the light source (L) and at least one signal-generating receiver (R) directed towards the detection zone. The opto-electronic device also has a reflector which includes (B) at least one narrow and approximately flat reflection area (15, 15', 15") extending essentially parallel to the longitudinal direction of the yarn and in the circumferential direction of the storage drum (3). The reflection area is bounded at its longitudinal sides by either a strip diaphragm fitted between the reflector (B) and the yarn passage plane (13), or diaphragmed regions (17) arranged approximately in the reflector plane.