Abstract: The weft yarn leaving a drum of a weft yarn store of a loom is monitored by a monitor device having at least two pairs of transmitters and receivers in a monitor ring which output signals to an evaluating unit (W) independently of one another in accordance with the number of yarn windings drawn off the drum. The dual delivery of signals is evaluated in an evaluation unit so that interfering signals can be distinguished from genuine malfunctionings, such as yarn breakages, so that unnecessary interruptions in operation can be avoided.