Abstract: An apparatus for detecting cracks in a flexible rotating coupling is disclosed in which the flexible coupling includes a flexible element having a plurality of flexible discs. An electrically conductive, normally continuous, line is affixed to at least one of the flexible discs and connected to a circuit. The conductive line becomes discontinuous if the disc cracks. The circuit is mounted on the coupling and transmits a signal indicative of the continuous or discontinuous condition of the conductive line and thereby the intact or cracked condition of the flexible disc. The transmitted signal is received by a stationary circuit which provides an output indication of the disc's intact or cracked condition.