Abstract: A worn brush indicator for machinery, e.g., a motor generator, wherein a carbon brush is in engagement with a moving contactor, e.g., a commutator or slip ring. The brush is made with an elongated cavity, and an insulated conductor is placed in the cavity. When the brush is worn to a point where the cavity is exposed and the insulating is worn away, the conductive member, having a carbon tip, engages the commutator, and an alarm circuit connected between the conductive member and the brush proper signals a worn brush condition.