Abstract: Apparatus for detecting when the tying mechanism of a baler has failed to properly tie a cord or wire around a bale which has been formed in the baler, and further for producing an alarm for the operator of the baler that the tying mechanism is not functioning properly. The apparatus includes a sensor needle which is mounted for pivotal movement over one of the surfaces of the bale and beneath the tying cord which extends lengthwise along the surface of the bale of material which is being formed. If the tying mechanism has securely knotted the cord around the bale of material, the tied cord will engage the sensor needle and pivot the sensor needle back as the tied bale moves towards the discharge end of the bale forming chute. A clock mechanism is provided which activates an alarm if the sensor needle is not engaged and swung back within a preset time interval.