In America’s early years, common ways of communicating emergencies may have been mostly ringing church bells or people sending messages by riding horses. Later, as technology developed, the telegraph became an almost instant way of communicating. After that, radio communications, telephones and sirens became common. After the surprise attack on Pearl Harbor, by the Japanese in 1941, Civil Defense sirens became popular and were used in many military bases and towns across America. A weakness of these systems is that they were not really able to tell people what they should do.