Enhanced 911

Enhanced 911 service or E911 service is a North American telephone network feature that automatically associates the physical address with the calling party's telephone number. This is generally done by a form of reverse telephone directory that is supplied by the telephone company. This provides emergency responders with the location of the emergency without the person calling for help having to provide it. Enhanced 911 has been deployed in most metropolitan areas in the United States. In some places (e.g., Minneapolis/St. Paul) it has been used since the early 1980s, though, as of the end of 2002 it was not available in every area.

The system only works in North America if the emergency telephone number 911 is called. Calls made to other telephone numbers, even though they may be listed as an emergency telephone number may not permit this feature to function correctly.

There is special privacy legislation that permits emergency responders to obtain the caller's information. Even though the caller's number may be blocked for caller ID purposes, the callers details will be provided to the emergency services.

A second phase of Enhanced 911 service is to allow a wireless or mobile telephone to be located geographically using some form of radio triangulation from the cellular radio network or by using a Global Positioning System built into the phone itself. There are also other proposed features that are intended to allow telephone callers from large corporate telephone networks to be located down to the specific office on a particular floor of a building.

In all cases, the location information provided is normally integrated into emergency dispatch centre's Computer-Assisted Dispatch or CAD system, to provide the dispatcher with an on screen street map that highlights the callers position and the nearest available emergency responders.

In other countries this type of facility is often called caller location, though its implementation is dependent on how the telephone network processes emergency calls.