The American 9 1 1 alarm telephone was born in the 1960s. 1967, the president's commission on law enforcement and judicial administration suggested that a unified telephone number should be set up throughout the country so that people can report emergencies in time. At&T soon announced that it chose 9 1 1 as the emergency number. 1In February, 968, the first 9 1 1 alarm station in China was established in Halliwell, Alabama. After 1970s, the number of 9 1 1 alarm telephones began to increase greatly. At 1976, 17% of Americans can call this number, which rose to 26% at 1979, rose to 50% at 1987, and now it has reached 85%. About 50% of the land area in the United States has been connected to the 9 1 1 number, 95% of which are enhanced systems that can provide the name and location information of each caller.
This is why terrorists chose 9. 1 1 to attack it.