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[Discuss] GPS feature in cellphones?

Rich Braun wrote:
> I'm not buying the NSA's published FUD on this issue.

Me neither.

This is also a knowable answer that any high-school level electronics
student can answer:

1. Monitor the current draw from the device's battery when the unit is
powered off. If you never see more an micro amps being drawn then you
can be assured that the RF power amplifier in the phone is not being used.

2. Place the powered off device next to an RF spectrum analyzer and
monitor for any transmission during a 24 hour period.

Repeat #1 and #2 for a variety of devices.

Even if they get around #1 by slowly charging a super cap, and sending
rare bursts of RF, #2 will still catch that. (Use a digital, logging
spectrum analyzer, A.K.A. a software defined radio.)

Anyone care to run the test? If Rich Pieri proves to be right, you'll be
guaranteed to get your name reported in the press world-wide for your

My guess is that the origin of this FUD comes from phones that have been
hacked by a government agency. One can imagine how it would be easy to
modify a phone's software such that the power button merely fakes a shut
down. Meanwhile it stays running, tracking, and sending audio from the
mic. It could even be more sophisticated: presumably modern smartphones,
even when off, run a small amount of code in a supervisory CPU to
monitor charging. That firmware might also get hacked to cause the
device to periodically wake up while the user is unaware.

The reason why the basic tests I mentioned above wouldn't have uncovered
this would be because this code only runs on phones of targeted individuals.

The only reason why pulling the battery out of your phone makes sense if
if you don't know if, or suspect that you are a targeted individual.

I wouldn't rule it out, but I'm also skeptical that the $20 flip-phones
you can still find at drug stores for pre-paid services contain GPS
receivers. Not just because of cost reasons, but also power drain from
their relatively small batteries. It seems more likely that the telecom
industry would have lobbied the FCC to get such low-end devices
grandfathered in such that they only require cell tower triangulation.
(The telecom industry pretty much gets out of anything that'll cost them
more this way.)

Richard Pieri wrote:
> This is basic radio. There's nothing fancy here.

The power section of a cell radio still requires hundreds of milliwatts
to reach a cell tower. You can't escape physics.

>> The average common-crook can get away from the cops by turning off his
>> cellphone...
> One word: Stingray.

A stingray has short range. They help you identify the house or
apartment the suspect is in, if you know the neighborhood or building.
They don't help you find the neighborhood.

Plus, per above, an off phone won't be pinging a cell tower.

You too can build your own "stingray." Not a real one that acts as a
cell tower, but an open WiFi hot spot that promiscuously accepts
connections from any device and logs identifying information. Some
retailers now do this to tracker passersby. Want to know if that corner
is a good spot for your next Starbucks? Monitor it for a few weeks, and
do a demographic extrapolation from the number of iPhones, Androids, and
whatever else you capture.


Tom Metro
The Perl Shop, Newton, MA, USA
"Predictable On-demand Perl Consulting."

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