3 ms·

Because iPhones can't ping each other when one's inside a Faraday cage.

nobodyandproud 2y ago
You're probably right, but wouldn't intermittent audio sidestep a faraday cage? Edit: I noticed it's "box" and not "cage" but I think the same what-if applies here.
- kstrauser 2y ago
  Anything's possible, but I am highly skeptical of the notion. Their little speakers don't have infinite frequency response, and I haven't heard reports of young teens saying their phones make weird chirps. Also, why on Earth would Apple do this? The notion that iPhone A in AFU mode is anxiously listening for iPhone B to come along and send it an audio trigger that it should reboot is hard to believe. It would be way easier to just tell iPhone A to reboot after N hours in AFU mode if they wanted to accomplish such a thing. And why would iPhone B be sending the "OMG reboot yourself!" audio signal to iPhone A in the first place?
  - superb_dev 2y ago
    They don’t need infinite frequency response, and I don’t think it’s unusual to have a frequency response outside of human hearing. I know for a fact that Cisco uses frequencies outside human hearing to help pair your computer to meeting room screens
bigfatkitten 2y ago
Faraday cages used by law enforcement, such as [1] aren't impervious to RF. They provide enough attenuation to keep phones off the cellular network and prevent GNSS from working, but not enough to prevent communication with nearby devices via Bluetooth or wifi. [1] https://ramseytest.com/rf-shielded/forensic-enclosure/ https://ramseytest.com/rf-shielded/forensic-enclosure/
- lxgr 2y ago
  That sounds implausible. A Faraday cage is an attenuator, which multiplicatively decreases signal strength by some constant (at least within a similar frequency band, which Bluetooth and 5G can be considered to be). Unless the forensic lab has additional special shielding from cell towers, the received strength of both a reasonably close cell tower and a nearby Bluetooth transmitter would be pretty similar, so they'd both be attenuated similarly.
  - JumpCrisscross 2y ago
    I assumed they have one cage they toss all the phones in.
    - lxgr 2y ago
      Ah, then they could definitely communicate with each other. And while I don't expect stock iPhones to do anything like what's being suggested in the article, I could see custom software activating a "panic mode" based on observations that plausibly suggest a device being in such an environment.
  - bigfatkitten 2y ago
    > That sounds implausible. I can say from experience that it is not. > A Faraday cage is an attenuator, which multiplicatively decreases signal strength by some constant It's not constant at all. The level of attenuation varies greatly based on frequency. For the Ramsey STE3000 I have here, it varies by 40dB or more at the frequencies at which I've tested it. The enclosure good for around -100dB at 700MHz, but only -60dB or so at 2.4GHz. > (at least within a similar frequency band, which Bluetooth and 5G can be considered to be). Even if you exclude mmWave and consider only the sub-6 bands, AT&T for example has LTE and 5G bands from 700MHz to 3700MHz. They're not similar at all. Worlds of difference in terms of propagation characteristics. > the received strength of both a reasonably close cell tower and a nearby Bluetooth transmitter would be pretty similar No, they wouldn't. On my Pixel 8 Pro right now I'm seeing -93dBm from a tower about half a mile down the road (700MHz LTE), and -40dBm from the BLE radio in the HVAC controller on the wall of this room, about 8 or 10 feet away. That's a 53dB difference. If I put my phone in the box, it attenuates the LTE downlink from down the street to well below the thermal noise floor. It cannot do the same for BLE; my phone can still talk to the HVAC controller from inside.

You're probably right, but wouldn't intermittent audio sidestep a faraday cage? Edit: I noticed it's "box" and not "cage" but I think the same what-if applies here.

kstrauser 2y ago
Anything's possible, but I am highly skeptical of the notion. Their little speakers don't have infinite frequency response, and I haven't heard reports of young teens saying their phones make weird chirps. Also, why on Earth would Apple do this? The notion that iPhone A in AFU mode is anxiously listening for iPhone B to come along and send it an audio trigger that it should reboot is hard to believe. It would be way easier to just tell iPhone A to reboot after N hours in AFU mode if they wanted to accomplish such a thing. And why would iPhone B be sending the "OMG reboot yourself!" audio signal to iPhone A in the first place?
- superb_dev 2y ago
  They don’t need infinite frequency response, and I don’t think it’s unusual to have a frequency response outside of human hearing. I know for a fact that Cisco uses frequencies outside human hearing to help pair your computer to meeting room screens

bigfatkitten 2y ago

Faraday cages used by law enforcement, such as [1] aren't impervious to RF. They provide enough attenuation to keep phones off the cellular network and prevent GNSS from working, but not enough to prevent communication with nearby devices via Bluetooth or wifi. [1] https://ramseytest.com/rf-shielded/forensic-enclosure/ https://ramseytest.com/rf-shielded/forensic-enclosure/

lxgr 2y ago
That sounds implausible. A Faraday cage is an attenuator, which multiplicatively decreases signal strength by some constant (at least within a similar frequency band, which Bluetooth and 5G can be considered to be). Unless the forensic lab has additional special shielding from cell towers, the received strength of both a reasonably close cell tower and a nearby Bluetooth transmitter would be pretty similar, so they'd both be attenuated similarly.
- JumpCrisscross 2y ago
  I assumed they have one cage they toss all the phones in.
  - lxgr 2y ago
    Ah, then they could definitely communicate with each other. And while I don't expect stock iPhones to do anything like what's being suggested in the article, I could see custom software activating a "panic mode" based on observations that plausibly suggest a device being in such an environment.
- bigfatkitten 2y ago
  > That sounds implausible. I can say from experience that it is not. > A Faraday cage is an attenuator, which multiplicatively decreases signal strength by some constant It's not constant at all. The level of attenuation varies greatly based on frequency. For the Ramsey STE3000 I have here, it varies by 40dB or more at the frequencies at which I've tested it. The enclosure good for around -100dB at 700MHz, but only -60dB or so at 2.4GHz. > (at least within a similar frequency band, which Bluetooth and 5G can be considered to be). Even if you exclude mmWave and consider only the sub-6 bands, AT&T for example has LTE and 5G bands from 700MHz to 3700MHz. They're not similar at all. Worlds of difference in terms of propagation characteristics. > the received strength of both a reasonably close cell tower and a nearby Bluetooth transmitter would be pretty similar No, they wouldn't. On my Pixel 8 Pro right now I'm seeing -93dBm from a tower about half a mile down the road (700MHz LTE), and -40dBm from the BLE radio in the HVAC controller on the wall of this room, about 8 or 10 feet away. That's a 53dB difference. If I put my phone in the box, it attenuates the LTE downlink from down the street to well below the thermal noise floor. It cannot do the same for BLE; my phone can still talk to the HVAC controller from inside.