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Comment by aja12 | Hacker News Reader

Baseband SoC running their own OS independent from Android/iOS and staying asleep (while still listening for incoming signals) is very much no longer in conspiracy theory territory and more an established fact now. I don't have the source at hand but it's in one of the standards. And the purpose is very clear: LEA like Interpol must be able to locate any IMEI at any point if in tower range, regardless of the power state of the "main" OS

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Surely this is really easy to prove by putting a phone into an anechoic chamber and using a spectrum analyser to show that it's still TXing?

The phone isn't going to connect to a tower it cannot see.

It can't just scream out into the void and hope a tower picks it up, it needs a few pieces of timing information & cell configuration beforehand.

I don’t doubt SoCs have their own micro-OS, but I too would love to see a reliable source showing phones connect to towers when powered off. Wouldn’t this, at a minimum, violate FAA/EASA rules? Google tells me the cellular radio in an iPhone has no power when in airplane mode or when off.

Even in airplane mode?

I dare you to do the following:

Charge phone to full 100%. Turn it off.

Put it into a faraday cage, e.g. a steel box, for 7 days.

Take it out again and wonder why the battery is empty.

(The faraday cage has the effect of making the modem have to switch bands constantly, which costs more electricity than sleep mode in LTE)

It would still be simpler for you to link to a credible source. A bit strange that you seem uninterested in doing so, and prefer to tell people to do their own experiments, in this case one that requires an extra phone and a week of time.

Batteries naturally drain slowly when not used. What would this little experiment prove, exactly?

Interesting, but you should probably use a control. Two phones, same hardware, same software. One inside the faraday cage, one outside, both in the same room with the same conditions otherwise.

Repeat the experiment a few times. Then cross over: liberate the caged phone, cage the free phone, and repeat the experiment a few more times. Or alternate the phones' positions between experiments. This mitigates hardware and software differences that might've been overlooked (such as a faulty battery, etc).

Analyze the results, draw your conclusions, publish, and encourage others to reproduce.

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