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Comment by lxgr | Hacker News Reader

> “As far as we know, the only thing that definitely stops Bluetooth beacons is turning off your phone,” Bhaskar said.

At least for recent Apple devices, that's not true anymore (intentionally, as it is used to support "Find my iPhone" even with a dead battery or on a phone that's been switched off):

https://arxiv.org/abs/2205.06114

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FWIW, this can be capability can be disabled when you power down the device. Not sure if you can make it a persistent preference or if you have to do it every time, though.

That's a setting you can turn off in iOS

I just looked it up and apparently this feature continues to work even in airplane mode. That seems crazy to me that doing that is even legal. What good is airplane mode if it doesn't actually disable all onboard radios? I get that it's theater and mobile device radios don't really interfere with airplane takeoff and landing anyway, but given the rule still exists, why are all iPhone owners allowed to ignore it because their devices don't support turning off the radios?

In Android turning "off" bluetooth and wifi just puts them in listen-only mode and this has been true for a long, long time.

Zebra devices have always-on bluetooth beacon capability, and even a second bluetooth radio in the battery(!): https://techdocs.zebra.com/emdk-for-android/9-1/mx/beaconmgr...

Where did you find confirmation that "Find my" still broadcasts in airplane mode?

Faraday bags

No need. There's a real off mode.

How do you invoke the real off mode?

My googling hasn't brought me the answer here. How do you do this?

A hammer, perhaps?

Fortunately, convenient and cheap with tasty contents!

https://arstechnica.com/information-technology/2017/11/austr...

According to that article, it looks like the bags have to be grounded to work:

"Snack packets are made with a foil that combines aluminum and mylar plastic, making them electrically conductive and ideal as a temporary electromagnetic shield for mobile devices—as long as the packet is closed and grounded—and you don't mind a few crumbs on your device."

I'm not sure if that's really true, or why that is... and if it is, how one could do it while on the move.

Yeah, my understanding of the faraday cage property is that it equalizes the charge across the surface.

Whether that charge is equal to ground or not is irrelevant I thought.

I will make the sacrifice tonight and eat a packet of chips for testing I guess. It is a hard life.

If it's not grounded charge will accumulate on the exterior walls but I doubt it will be significant for a cellphone.

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