Warning signals are used to alert people of potential danger or to warn them of an impending event. Common warning signals include SIRENS, alerts, alarms, and OMENS. SIRENS are loud, high-pitched sounds that are used to signal an emergency. Alerts are messages sent out to inform people of a potential danger or to warn them of an upcoming event. Alarms are devices that make a loud noise when triggered, usually to alert people of a potential danger. OMENS are signs or symbols that are believed to foretell the future.