In the earliest days of the telephone, calls had to go through an operator. The caller might say, "I'd like to report a fire." Operators knew the location of the caller and sometimes activated the town's alarms.

That changed with the introduction of the dial phone. Often callers didn't know what numbers to call for the police or fire.

In 1968, the federal government and AT&T agreed to designate 911 for emergency calls. It was originally advertised as "nine-eleven," but was changed to "nine-one-one" because some callers, especially children, might waste time looking for an "eleven" button.

More than 240 million 911 calls are dialed in the U.S. each year, making public safety communications a way of life for all Americans.

Click here for more information on 911 training.