Re: Location tracking in cellphones

["Rob, grandpa of Ryan, Trevor, Devon & Hannah" <rslade () sprint ca>]

Date sent:              Wed, 21 Sep 2005 19:16:33 -0400
From:                   David Dagon <dagon () cc gatech edu>

> On Wed, Sep 21, 2005 at 03:49:24PM -0400, Richard M. Smith wrote:
>
> > I'm curious now when other models of cellphones transmit location
> > information to carriers.

Richard, I'm not quite sure what your question relates to, so I'm not sure if I'm 
going to provide useful info.  Apologies if I seem to be talking down to you.

> http://www.spywareinfo.com/articles/cell_phones/

Some interesting and somewhat paranoid opining, but it doesn't seem to get into 
detail.

First off, all cell phones, when on, regularly (about every five minutes, I think) 
transmit an "I am here" type signal on one of the control bands for cell phones.  
(The control bands are not used for calls, but are used between the cell phones and 
towers to request or assign channels for calls.)  Cell towers receive this signal and 
jointly (through the switch) determine who has the strongest signal, which tends 
to indicate the nearest tower.  This info is stored in the cell system for distribution 
of incoming calls, and can be queried.  With proper software (not installed on all 
switches) this info can also be used to triangulate location to within about 100 
metres.  (For the tin foil hat crowd, this means you can be located any time your 
cell phone is on.  It is also the reason they tell you to turn cell phones off in 
hospitals and airplanes, even if you are not making a call.  It's really interesting to 
sit a cell phone near speaker wires and crank the volume.)

Newer phones also have GPS circuitry.  Theoretically this can be accurate to 
within a metre, but, given the size and situation of cell phones, I suspect that you 
wouldn't want to trust it to an accuracy of less than 100 metres either.  Most 
times it should locate to within about 10 metres.  Again, this info can be 
transmitted over the control channel with the regular "I am here" call.

E911 makes use of both types of location info, using the GPS by preference.  (I 
don't know if there is any sanity checking on it: presumably so.)

The new "Seek and Find" (Bell Canada's marketing name) systems that locate cell 
phones are quite interesting.  I did an article on the system, and got quite a detailed 
response from someone at Bell Canada.  Bottom line: the system is hackable, but 
there are some very neat provisions that making access to the data evident to the 
phone user.

======================  (quote inserted randomly by Pegasus Mailer)
rslade () vcn bc ca      slade () victoria tc ca      rslade () sun soci niu edu
               Your secrets are safe with me and all my friends.
http://victoria.tc.ca/techrev    or    http://sun.soci.niu.edu/~rslade

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