Attentional Control Theory suggests that acute stress reduces the efficiency of working memory and top-down control, increasing susceptibility to distraction. In contrast, Cognitive Reallocation accounts suggest that acute stress narrows attentional focus and potentially reduces distraction. We tested these competing predictions using a cross-modal oddball task, comparing participants exposed to an acute stressor, via a realistic firefighter training exercise, with an unstressed control group. Participants categorised visual targets preceded by either a standard sound or a rare deviant (a noise burst or a semantically congruent or incongruent word). Both groups were distracted by the deviant sounds, but the effect was larger in those exposed to the stressor, particularly early in the session. Over time, this difference diminished—consistent with recovery from stress exposure and stronger habituation in controls. These results indicate that acute stress is associated with heightened vulnerability to auditory distraction in a pattern resembling reduced working memory availability.