Australians have been warned that a nationwide test of a new emergency alert system could inadvertently expose secret second phones used for extramarital affairs or hidden by vulnerable people. On Monday 27 July at 2pm AEST, mobile phones across the country will emit a 10-second siren as part of a trial of AusAlert, a new warning system designed to signal bushfires, floods and other natural disasters ahead of its planned rollout in October.

The alert will be classified as a "critical alert", meaning recipients will not be able to silence or mute it in the usual way, raising concerns that phones kept hidden from partners or family members could suddenly and audibly reveal their existence. Commentators have flagged this as a risk both for people concealing infidelity and for vulnerable individuals, such as those in coercive or abusive situations, who may rely on a secret device for safety.