If you call the 911 on your cell phone they can identify your location to within 30 to 50 meters which is about about the same as 30 to 50 yards. I suspect that many cell phones have a backdoor entrance on them for the cops so they can get your cell phones to tell the police your location even when you don't call 911.
I think a standard GPS device needs to see 4 satellites before it can identify your location and 5 satellites before it can give you your alittude. But remember with cell phones the cops already have the location of at least one cellphone tower and maybe more so the cell phone GPS device doesn't need to see as many satellites to nail down your location.
December 01, 2008
Police say in a crisis, landlines are lifelines
by Meghan Moravcik Walbert - Dec. 1, 2008 12:00 AM
The Arizona Republic
As the economy worsens and families tighten household budgets, one of the first things to go is the traditional landline phone.
Instead, families rely on cellphones, which are convenient and cost-effective for long-distance calls.
But cellphones can be difficult for 911 operators to track and locate in an emergency. Valley police agencies differ on whether to advise people to keep a landline or to adapt to what appears to be an irreversible trend. Peoria's police department urges residents to keep landlines and traditional corded phones.
Corded phones can do things cordless phones can't, said Mike Tellef, a police spokesman. They remain active during power outages and their lines don't get overloaded, as cellphone towers can, with an influx of calls. The phone number's address is also easily traced.
If a cellphone tower is busy, calls go to the next open tower, Tellef said. In some cases, a caller could be located in Peoria but the call would be routed through a Glendale tower.
In those cases, emergency operators have to determine which city the caller is in and then transfer the call to the appropriate 911 center.
The additional time could mean emergency responders would arrive too late, Tellef said.
"It's not a lot of time, but it's still time," he said.
But several other Valley police agencies are focusing more on educating cellphone users to provide the most important information up front.
"They definitely need to tell us where they are," said Karen Allen, a communications administrator with the Tempe police.
Because 911 operators often can't pinpoint the exact location of a cellphone, callers need to stay on the line and give as much information as possible about their location, she said.
The technology is improving, but pinpointing locations of cellphone users isn't an exact science, and the accuracy depends upon the service provider and the cellphone.
Most 911 operators can generally pinpoint the location of a caller within 35 to 50 meters, unless the cellphone is particularly old, said Liz Graeber, a 911 administrator at the Maricopa Region 911 office.
Many service providers enable calls to be tracked with a GPS chip in the phone, the most accurate technology available, Graeber said.
Other providers use a "triangulation" method in which several cell towers use the signal to determine the latitude and longitude of the phone.
Training residents to immediately provide necessary information will help callers receive the fastest and best response, said Sgt. Jim Toomey, a Glendale police spokesman.
"Specifically, we want people, when calling 911, to say, 'I am at such-and-such a place, my name is XYZ, this is what is going on,' " he said.
But there are occasional cases in which callers are unable to tell an operator where they are located. And when a child calls, they do not always know the address.
It's because of calls like these that the Peoria police want all residents to keep corded phones.
Cellphones aren't the only kind of phones that can create locating issues. When someone calls 911 from a voice-over-Internet phone, the address at which the phone is registered will show up on the operator's screen. If the resident moves and doesn't update the address, the call could go to the wrong city.
Tellef said residents should be able to get basic phone service for about $15 a month. He said corded phones were particularly important for the elderly, disabled or those with young children.
Reporter Lisa Halverstadt contributed to this article.