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Comment by intc | Hacker News Reader

> It’s smart to avoid using wireless devices like mobile phones or GPS systems, since they have digital signatures...

Could someone explain how a GPS receiver (especially one which doesn't utilize DGPS of any sorts) would have any sort of digital signature which could be measured from a drone?

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Detection and Localization of Multiple R/C Electronic Devices Using Array Detectors[1]

Locating Noncooperative Radio Receivers Using Wideband Stimulated Emissions[2]

A Practical Superheterodyne-Receiver Detector Using Stimulated Emissions[3]

1. https://ieeexplore.ieee.org/abstract/document/6857348

2. https://ieeexplore.ieee.org/document/6329437

3. https://ieeexplore.ieee.org/document/5699393

The book Spycatcher details how, in the 50s, MI5 developed systems to detect radio receivers. They fitted out vans and drove past embassies to determine the frequencies different embassies were tuned into. I think they also tested with fitting out aircraft, but it’s a long time since I read the book.

Of course there is also the opinion that tv detector vans were a hoax and would never work, so ymmv :)

A good friend of mine had the chance to see such a van while working for the French Navy. The operator even showed him a (somewhat blurry) real-time view of my friend's Mac desktop in the building next door... (This happened in the early 90s in Toulon arsenal).

That sounds like Tempest, and I somehow doubt that they actually showed him that.

Why not? They didn't explain how it works. And he was an officer at the time.

It's not that Tempest was ever a secret, There was advertising for countermeasures (metal screens for Windows, just like you have in your microwave) in the mid 1980s.

Spy satellites aren't a secret either but it was big news when Trump revealed their resolution capability.

They are analog signals right, rather than digital signatures. I think the author has conflated GPS receivers with smartphones that use them.

There's a few ways to detect radio receivers, some of them based on listening for incidentally radiated intermediate frequencies (which have to be a multiple of the received frequency) from the amplifier in the receiver: https://en.wikipedia.org/wiki/TV_detector_van

It would be a heck of a trick to detect a GPS receiver that way, though. Probably be easier just to listen for the RF noise from the switching regulator in the power supply.

> Probably be easier just to listen for the RF noise from the switching regulator in the power supply.

Natural things give off very little RF... Pretty much anything electronic gives off far far more. It doesn't seem out of the realm of possibility for a military to use antenna arrays to try to track every nearby electronic device of any kind. Sure - identifying the device might be tricky, but you gain a lot of intel simply knowing where electronic devices are clustering and headed.

Most of the methods listed there were listening for the EM of the TV being on, not the reciever antenna. Technically, it sounds like they wouldn't be able to tell the difference between pirated TV and watching a movie on the VCR.

I think the reasoning for those TV-sniffing trucks at the time were not what you watch, but that you could watch at all, i.e. you had a device capable of watching TV and to pay your damn dues for that "privilege".

That is one of those sentences in an article where you wonder...

"Did the author know very little about the subject, or does he know exactly what he has written?"

My guess would be that they use the same technique as radar-detector-detectors. Essentially sniffing out the RF radiation emitted by an RF receiver

  https://en.m.wikipedia.org/wiki/Radar_detector_detector

Any antenna is both a receiver and a sender, like a mic/speaker.

From Garmin website, first category (wearables), first item:

https://buy.garmin.com/en-US/US/p/702902#specs: CONNECTIVITY Bluetooth®, ANT+®, Wi-Fi®.

From Garmin website, featured items:

https://buy.garmin.com/en-US/US/p/711488: CONNECTIVITY Bluetooth®

https://buy.garmin.com/en-US/US/p/707174/pn/010-02427-02: CONNECTIVITY Bluetooth®, ANT+®

https://buy.garmin.com/en-US/US/p/713363: CONNECTIVITY Bluetooth®, ANT+®, Wi-Fi®

Older school hiking GPS:

https://buy.garmin.com/en-US/US/p/699779: WIRELESS CONNECTIVITY yes (Wi-Fi®, BLUETOOTH®, ANT+®)

The weighting scale apparently has no wifi, so that's drone safe. Though not quite portable.

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