Editing Enhanced 911 (section)

===Wireless transmission===
In parallel to the actual voice call, the ALI database gets periodically updated with more precise and recent location information.<ref name=":3" /> Cellular networks can determine a more precise location of the caller's device by using triangulation from the cell towers ([[radiolocation]]). In addition to triangulation, a second source of location information may be the caller's phone itself (or other cellular device).

Many phones manufactured after 2005 have [[Global Positioning System|GPS]] receivers built in.<ref>{{Cite news|url=https://electronics.howstuffworks.com/gps-phone2.htm|title=How GPS Phones Work|date=2005-10-24|work=HowStuffWorks|access-date=2018-10-05|language=en}}</ref> When the cellular phone detects that the user is placing an emergency call, it begins to transmit its location to a secure server, from which the PSAP can retrieve it. Cellphone manufacturers may program the phone to enable GPS function automatically (in case it has been turned off) when the user places an emergency call.<ref name=":4" />

For wireless calls, the ANI (or "pseudo-ANI") is a unique number assigned to each individual 911 call, assigned at a mobile switching center.<ref name=":3" />