The study of animal communication during predator encounters has provided insights into the function of kin selection, the ontogeny of vocal development, and the mechanism of predator recognition. Less attention has been devoted to the study of geographic variation in alarm vocalisation behaviour. Here, we describe an alarm song produced by Superb Fairy-wrens (Malurus cyaneus) under immediate threat of predation. We quantify geographic and individual variation in alarm song. Next, we used playback experiments to measure the effect of familiar versus unfamiliar alarm song on the response of the pair partner to its mate's alarm song. We found both geographic (element frequencies across sites) and sex-based (females had larger bandwidth) differences in alarm song. Playback of the alarm song evoked distinct anti-predator behavioural responses, whereby the alarm song of mates evoked stronger alarm responses (faster latency to respond, longer latency to feed, more head movements, and change in vocalisation types) than those of unfamiliar birds. We discuss the benefits of geographic and individual variation in alarm song, which may be particularly favoured in long-lived sedentary species that form pair bonds.