On 4/23/2011 7:45 PM, Nancy Young wrote:
> Dan Abel wrote:
>
>> "Nancy Young" > wrote:
>
>>> Oddly, I don't have a problem with that, you need to pick up
>>> a signal to place a call. I don't think you even need to make a
>>> call for there to be a record kept by the companies where police
>>> can get to it if there's some reason.
>>
>> Plus, most people don't just want to make calls on their cell phones,
>> they want to be able to receive calls. So, as soon as you turn on
>> your cell phone, it does a scan for the most powerful (closest)
>> signal. Once it finds it, it sends out your phone id to that tower,
>> and it is entered into a database, so when somebody calls you, that
>> call can be routed to the tower that your phone is now listening to.
>
> Of course, it makes perfect sense when you put it that way. What
> I know I picked up from watch true crime stuff and got the idea you just
> needed your phone turned on for them to find out whereabouts
> you were.
> nancy

The actual mechanism is called "autonomous registration". As Dan
described your phone registers itself when you first turn it on and then
periodically "re-registers" itself whenever it is on so the system can
pass a call to your handset or even know if you are roaming on another
system so it knows who to hand off the call to. That location
information is nowhere near like you see on the CSI shows where they
declare "OK, pick him up, he is on 59th st halfway between 5th and 6th
Avenue." Basically cellsites are sectorized into 3, 120 degree sectors
so it knows roughly where you are in a sector.