What happens when I call 9-1-1 from a cell phone?
You’ve found yourself in an emergency. You’re in a situation where you’re injured, someone else is injured, there is a good chance of someone getting injured or someone is trying to injure or kill someone else. So what do you do? You pull out your cell phone, you flip it open, slide it open or touch the screen and you call 9-1-1.
When The Dispatcher Answers The Phone…
Now depending on your cell phone carrier, the the area you’re calling from and other conditions, you’re 9-1-1 call will come across to the dispatcher as either phase 1 or phase 2.
- Phase 1 – The dispatcher receives the cell-phone number of the 9-1-1 caller and the location of the cell-tower antenna the phone is using. The call is routed to the PSAP nearest to that tower. Here is an example of what the dispatcher sees on our map:
This map shows that the caller was somewhere south-west of the cell tower at 3455 S. Corona. This information may be helpful if you make a call in a rural area, but in an area like the densely populated area like the one pictured, it’s not much help at all. The dispatcher is still going to depend on you to tell them where you are. The only other information the dispatcher receives is the name of your cell phone carrier.
- Phase 2 – The dispatcher receives the cell-phone number and the location of caller to an accuracy of 50 to 300 meters depending the type of location system being used by the wireless provider. The call is routed to the PSAP nearest to that location or nearest to the cell antenna in use. Here are 2 examples of what the dispatcher may see on a phase 2 call:
The first map shows a call from a phase 2 phone with a 182 meter confidence radius. While the caller was probably on Vassar between Lafayette and Humboldt, the caller could be anywhere within that red circle. This was probably caused because the caller was moving in a vehicle, but the dispatcher can not assume your location. The dispatcher is still going to depend on you to tell them where you are.
The second map shows a call from a phase 2 phone with a 9 meter confidence radius. This caller was almost definitely in the exact location shown on the map. Technology isn’t perfect though. The caller could’ve been in the building north of the phone icon, but the map was just a bit off. Once again, the dispatcher is going to depend on you to tell them where you are.
Just like with phase 1 calls, the only other info dispatchers receive is the carrier of the cell phone.
How Does The Call Get To The PSAP?
A phase 2 cell phone will attempt to figure out where it is when the 911 call is made. If the cell phone uses GPS, it’s considered handset-based and uses satellites to find out where it is. If the phone uses cell phone towers, it’s considered network-based. Both techniques uses a process called trilateration to come up with a location. If the process doesn’t work, the call will come in as phase 1.
Conclusion
As cool as technology gets, we will never fully depend on it to help people. An icon on a computer can help find a caller and we will depend on that information if we absolutely have to depend on it. There are also times when a caller doesn’t have a good idea on their location. A good mix of technology and people can help dispatchers get help to you as fast as possible.
Up Next: What happens when I call 9-1-1 from a VOIP phone?
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Tags: 9-1-1, 911, cell phone, cell phone towers, dispatchers, GPS, phase 1, phase 2, PSAP
Public Safety | 
Scott Pantall | December 26, 2009
By R Walker, December 28, 2009 @ 4:02 am
What mapping system is that? I work for Sequatchie County 911 (Sequatchie County, TN) and we have GeoLynx, but whatever you’ve got images of here look MUCH more efficient…
By Scott Pantall, December 28, 2009 @ 4:57 am
Thanks for the comment! We use Contact One’s QuickPoint, http://www.contactone.com/prod_quickpoint.htm. It’s the only mapping software I’ve used, so it’s nice to hear that someone is envious of it.
I’ve only worked for one agency, so I hope my post reflects what info other dispatchers see too.