Impact events on composite structures that may cause damage can be readily detected and located using sensors that respond to the resulting impact stress waves as they propagate. This capability can be used as an alert to maintainers or operators who use the structures that an incident has occurred. However, for this capability to be truly useful it must include the capacity to determine automatically if the impact has caused damage. This will avoid the situation where a follow up inspection of the impact site reveals that no damage has been caused (no-fault found). This paper reports results from impact tests on glass and carbon composite, structural test specimens in which impact sensor data has been processed to reveal clear features that allow discrimination between damaging and non-damaging impacts. The sensors employed were bonded to the specimens and they detected stress and acoustic waves generated by impacts over a broad range of frequencies (bandwidths in excess of 100kHz).This could provide maintainers and operators with a quasi, real-time monitoring capability indicating occurrence, location and consequences of accidental impacts.