Abstract: A bag closing container device applies a strip of closure tape to a container, and sews stitches through the tape and container walls, as the container is moved past a closure station. A first sensor, located near an encoder disc driven by the container transport motor, generates a signal proportional to the container transport speed. An idler roller frictionally engaged with the closure tape carries an indicator wheel, which generates in a second sensor a signal proportional to the tape speed. The thread used in stitching the containers is wrapped around a detector wheel on its way to the closure station, and is frictionally engaged with the wheel. Wheel rotation generates in a third sensor a signal proportional to thread speed. The device includes a microprocessor which receives the signals as inputs, continually compares container transport speed and thread speed, and generates a thread fault indication if the thread and container speeds deviate from a preselected ratio.