Abstract: At a channel bank, such as a D-type channel bank used in the Bell System, a steady visual alarm is exhibited if the source of a detected failure is at a location either within the channel bank or in the digital hierarchy of a digital transmission network. Unfortunately, a craftsperson is unable to distinguish between the two failure locations. To distinguish between the locations, apparatus for indicating the failure location to be in the hierarchy is situated between the hierarchy and the channel bank and, responsive to an alarm failure signal from the hierarchy, extends a predetermined cyclic code signal to the channel bank. Without modification of the channel bank and responsive to the code signal, a cyclic visual alarm in lieu of the prior art steady alarm is provided thereat.