Air raid alert, also known as an air raid warning, is a notification that warns people of an impending attack. This phrase originated during World War II when enemy air forces used to warn of impending attacks on urban areas. Some synonyms for air raid alert include: 1. Alarm bells: This indicates a loud and urgent warning, people must act immediately. 2. Siren: Typically, sirens are used to alert people of an emergency. The sound is restricted to specific frequency to notify the public. 3. Invasion warning: Invasion warning advises people to seek shelter or take other protective measures. 4. Red alert: This is an urgent warning given when there is an impending danger. 5. Emergency signal: This signal has a long history that was used as a warning for impending bombardment or air raids. Air raid alerts are used in times of war where the safety and well-being of people need to be taken into consideration.