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Replies to "Your cell phone is probably a GPS tracking device"

Previous Politech message:


Date: 06 Aug 2003 16:22:55 +1200
From: Steve Withers <swithers@mmp.org.nz>
To: Declan McCullagh <declan@well.com>
Subject: Re: FC: Your cell phone is probably a GPS tracking device

Who wants to carry a homing beacon for the Department of Homeland

Steve Withers <swithers@mmp.org.nz>


Date: Wed, 6 Aug 2003 06:12:59 +0200 (CEST)
From: Thomas Shaddack <shaddack@ns.arachne.cz>
To: Declan McCullagh <declan@well.com>
Subject: Re: FC: Your cell phone is probably a GPS tracking device

If the phone tracking is only for 911 service, as declared, there is no
reason why the carriers should be updated about its position at all times.

Why not make the phone firmware to keep its position to itself, and
disclose it only when 9-1-1 is dialed? Then only the 911 service will get
the location data, and privacy (within the limit of cell density of the
network, which is unpleasantly accurate but still orders of magnitude
less precise than GPS) is maintained for all other operations.

That so simple solution wasn't selected suggests possible "side
intentions" with the realtime location data, being it profiling of people
by law enforcement agencies, or just "mere" annoying with advertising.

However, self-help could still be possible. You may take the risk and give
up on the 911 getting your position and physically damage the telephone;
you may remove or disable the chip, or if it'd be too tightly integrated
with the rest of the phone maybe adversely affecting the antenna gain in
the GPS band could help as well (eg, a bandpass filter?). Or you may be
more selective, and make a tiny GPS jammer with very low output power,
that would feed its output directly into the phone's receiving antenna, or
to its immediate vicinity; that way you will jam only your own phone
without adversely affecting anything more than a foot away. As a
beneficial side effect, the lower output power you use, the less it eats
the batteries. Possibly a low-power variety of the one published in Phrack
60. The GPS coverage, especially in buildings and tunnels, is so bad that
the telcos can't link their service to active GPS positional reporting.

The easiest way, if the phone construction allows it, is a modification
with a small switch on the phone case, connected to some circuit inside
the phone that disables the GPS signal reception. May be as simple as
disabling the chip's clock, flipping the GPS_RECEPTION_ENABLE signal (if
available on the chip's pins) or connecting a filter to the antenna. Then
you have both: the telco gets your location data only when you need it.
Caveat: GPS needs sometimes up to couple minutes to acquire its position.
That's good to keep in mind for case you'd need to supply the position.

The hope looks quite like a soldering iron tip.


Date: Wed, 6 Aug 2003 06:30:03 +0200 (CEST)
From: Thomas Shaddack <shaddack@ns.arachne.cz>
To: Declan McCullagh <declan@well.com>
Subject: Re: FC: Your cell phone is probably a GPS tracking device

One more comment to the article:

At the end of the article, the author states:

     Trouble is, this doesn't really shut off the GPS chip*the satellites
     still know where you are. They just won't remind you of that fact.

That's not true. The satellites are transmitters-only; there is no way how
the receiver on the ground can relay its position to the GPS satellites.
For telling the position to somewhere else, a transmitter or transceiver
of some kind is necessary. The GPS chipset itself is receive-only.

Of course, one then would like some assurance that the phone's firmware
really keeps the data for itself when the I-Am-Here button isn't pressed.
But that is something only someone equipped with cellular protocol
analyzer (or someone reverse-engineering the phone's firmware) can answer


Date: Tue, 5 Aug 2003 23:10:52 -0600
From: Trammell Hudson <hudson@swcp.com>
To: Declan McCullagh <declan@well.com>
Cc: monty@roscom.com
Subject: Re: FC: Your cell phone is probably a GPS tracking device

Hash: SHA1

[ Warning: Technical digression ]

Monty Solomon <monty@roscom.com> wrote:
> [...] What your salesman probably failed to tell you-and may not even 
> realize-is that an E911-capable phone can give your wireless carrier 
> continual updates on your location. The phone is embedded with a 
> Global Positioning System chip, which can calculate your coordinates 
> to within a few yards by receiving signals from satellites. [...]

E911 does require that the mobile phone carrier be able to pinpoint
the location of the phone to within a 50 meters for 67% of 911 calls
and within 150 meters for 95% of calls.  Logging position data and
making it available to LEO is not covered in the E911 mandate.

There are several techniques for computing the position, such as Cell of
Origin, Time Difference of Arrival, Angle of Arrival, Enhanced Observed
Time Difference, GPS and Network Assisted GPS (AGPS).

COO accuracy depends on the cell configuration and ranges from 100 m
for a low power city cell to 30 km for an analog cell out in
the country side.

TDOA is reasonably accurate, but requires synchronized clocks in all
towers.  This is not cost effective for most applications.

AOA is also fairly accurate, but does require extra equipment in
each tower.  However, it does not require an accurate clock, so it
costs less than TDOA.

Full GPS receivers in each phone are very expensive, require lots
of power and only work with a good view of the sky.  50 m accuracy
requires at least 3 good SVs in view.  While many customers would
really like this feature, I do not know of any phones in which it
has been implemented.

AGPS uses a reference GPS receiver in each tower that sends SV
data to the mobile handset.  The handset does not have a full GPS
installed; instead it uses the SV data to receive the time pulses from
a single SV and sends the time delta to the tower.  The tower is
then able to compute the position of the phone via a differential
calculation and log it for E991 compliance.  It is typically accurate
to 100 m indoors and 15 m outdoors.

Most new phones that are E911 capable or offer "Location Based Services"
are built with AGPS.  So they don't have a real GPS receiver that you
could use, but the network can determine your position.  It is a shame
that this data is not made available to the phone or the end user --
I would love to be able to write applications for my Treo that know
where it is without having to add a clusmy external GPS.

- -- 
  -----|----- hudson@osresearch.net                   W 240-283-1700
*>=====[]L\   hudson@rotomotion.com                   M 505-463-1896
'     -'-`-   http://www.swcp.com/~hudson/                    KC5RNF




Date: Wed, 6 Aug 2003 01:36:30 -0400 (EDT)
From: Timothy M. Lyons <lyons@digitalvoodoo.org>
To: Declan McCullagh <declan@well.com>
Subject: Re: [politech] FC: Your cell phone is probably a GPS tracking


In regards to Brendan's piece, he makes some interesting and valid points.  
However there are phones that permit the owner to select either a GPS mode of
E911 only or continuous.  As always it's up to the consumer to understand the
feature set of their mobile device and make purchase decisions based on their
personal requirements.  If enough consumers decide to only purchase phones 
with that functionality then I think you would see manufacturers scrambling to 
add that "feature."

I know my Verizon/LG VX4400 allows one to select the GPS (Location) mode by 
accessing the Location menu (option 8 off the main menu) and setting 



Date: Wed, 6 Aug 2003 01:50:48 -0400
From: Monty Solomon <monty@roscom.com>
To: Trammell Hudson <hudson@swcp.com>
Cc: Declan McCullagh <declan@well.com>
Subject: Re: FC: Your cell phone is probably a GPS tracking device

At 11:10 PM -0600 8/5/03, Trammell Hudson wrote:
>Full GPS receivers in each phone are very expensive, require lots
>of power and only work with a good view of the sky.  50 m accuracy
>requires at least 3 good SVs in view.  While many customers would
>really like this feature, I do not know of any phones in which it
>has been implemented.

The Motorola T-720 apparently has GPS



Date: Wed, 06 Aug 2003 03:17:20 -0400
From: Joanna Lane <jo-uk@rcn.com>
To: declan@well.com
Subject: RE: Your cell phone is probably a GPS tracking device

I know you don't post personal comments on politech, but the other side to
this story is that GPS saves lives. No self respecting teenager would be
seen without a cell phone with a GPS tracking device, it's this year's must
have accessory. Mothers will gladly trade information about where they get
their nails done if that's what it takes for our children to be found
quickly in 911 situation. When glow in the dark GPS wristbands for pre-teens
appeared, encumbered by a separate service contract, predictably they
crashed and burned. Not cool. Harnessing new cell phone technology as an aid
to self preservation for the most vulnerable in society is a good reason to
buy into it, notwithstanding that Verizon and T-mobile ought to be offering
an opt-out for everything other than the 911 function, so that you can never
know where I have my nails done, unless I tell you.

Joanna Lane


Date: Wed, 6 Aug 2003 03:20:54 -0700
From: Thomas Leavitt <thomasleavitt@hotmail.com>
To: declan@well.com
Subject: Re: Your cell phone is probably a GPS tracking device


Apparently, Korean women can track their husband's movements via their
cellphones. I also vaguely recall hearing something about wives being able
follow their husband's movements via some type of commonly carried wireless
device in Japan causing quite a bit of trouble.

Thomas Leavitt


Date: Wed, 6 Aug 2003 09:21:31 -0400
From: Richard M. Smith <rms@computerbytesman.com>
To: declan@well.com, Richard M. Smith <rms@computerbytesman.com>
Subject: RE: Your cell phone is probably a GPS tracking device

Hi Declan,

My wife recently got a new Kyocera 7135 Smartphone with a GPS receiver
in it.  According to the Kyocera manual, the default for the phone is to
only send out location information on 911 calls.  However, when I was
setting up the phone for my wife, I noticed that the location setting
was changed to send out location position on all calls.  My guess is
that this change was made by Verizon Wireless before we ever picked up
the phone. 

I'm not sure what Verizon's thinking is here, but I find it pretty
annoying that we now have to do privacy audits on our cellphones to make
sure companies are doing what they say. 

Other 7135 owners can check the GPS setting themselves by clicking on
"Phone Prefs" from the Palm home page, selecting "Phone Service" from
the drop down menu, and making sure that "Position Location" is set to
"911 Only".

On the flip side of things, the 7135 is the perfect location tracking
device.  Because it is a Palm PDA as well as a cellphone, it shouldn't
be too difficult for a company to write a small application that logs
the GPS position once a minute.  A log file can uploaded later to a PC
and viewed in a mapping program.  Maybe this a new product idea for the
spousal spyware companies like SpectorSoft. ;-)

Richard M. Smith

[I recently bought a Nokia 3650 with GPS. At least the Kyocera phone lets
you disable it; if such a menu exists on the Nokia, I haven't found
it. --Declan]

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