Abstract: An apparatus for monitoring the underthread in sewing machines, in which at least one signal generator is mounted in the path of the underthread and is disposed to generate an electric signal when the underthread is urged by means of a looper against the signal generator, and the generated signal is coupled to a signal monitoring circuit electrically connected to the signal generator device and is operable to shutdown the machine in response to a loss of said signals from said signal generator device.

Abstract: Apparatus for detecting whether one thread selected from a number of threads is in motion, while no other thread is in motion, or whether a set of threads selected from a number of sets, each having two or more threads, is in motion, while no other set is in motion. The apparatus includes a signal generator associated with each thread for generating an electric signal in response to the movement of the associated thread. The signal generators are coupled sequentially to signal indication apparatus. If the prescribed thread movement is detected, the signal generating apparatus inhibits generation of an alarm indication. If the prescribed thread movement is not detected, the signal generating apparatus activates a trigger device to initiate an alarm.