Richard B. Gilbert wrote:
> JoeSpareBedroom wrote:
>> "George" <george@nospam.invalid> wrote in message
>> news:h201g9$irh$1@news.eternal-september.org...
>>> JoeSpareBedroom wrote:
>>>> My kid and two friends are going on a 3 week backpacking trip, and
>>>> all their phones have a GPS feature. (My son's phone is a Samsung
>>>> SCH-A950). Assuming the GPS feature has not been switched to "911
>>>> emergency only", and assuming the phone is in an active zone for the
>>>> carrier in question, is it possible for the carrier to ping a phone
>>>> and get an approximate location? I'm assuming no input from the
>>>> phone user, other than the fact that the phone is turned ON.
>>> Sure, no "ping" is involved. But do you have a question like "can I
>>> call them and ask where juniors relative position is"?
>>>
>>> Law enforcement can but don't know if you can.
>>>
>>> VZW actually has a subscription product called "chaperone" for end
>>> users:
>>>
>>> http://products.vzw.com/index.aspx?id=fnd_chaperone
>>
>>
>> Our idea is having law enforcement people track the phone. (TV cop
>> shows often exaggerate the possibilities of technology).
>>
>> So, no "ping". Do cell phones regularly make brief contact with the
>> nearest antenna, or something? And thanks for the Chaperone idea. Next
>> on the reading list.
>>
> I think a cell phone MUST send a "here I am" to the tower. Otherwise,
> how could you receive an incoming call? It hardly seems practical for
> the system to tell every tower in the U.S. that it's looking for you.

Its called "autonomous registration".