Alerting authorities may choose to distribute an “all-clear” message at their discretion once the situation has been resolved. The all-clear message would be distributed via broadcast services at their discretion but not necessarily wireless devices.
As part of an emergency alert message, alerting authorities must also set a time when they expect the alert to expire. The expiry time is different from the “all-clear” message, as it is set in advance and does not necessarily indicate when an emergency is over. Because each emergency alert issued requires that an expiry date and time be included, alerting authorities estimate when they think the alert will need to be updated or cancelled.