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> The digital forensics lab that noticed the issue had several iPhones in AFU state reboot, including iPhones in Airplane mode and one in a faraday box. You ca

> The digital forensics lab that noticed the issue had several iPhones in AFU state reboot, including iPhones in Airplane mode and one in a faraday box. You can stop reading there. iOS 18 doesn't add freaking telepathy to phones. Whether it's a bug or a new feature Apple added that reboots phones under certain circumstances, it's not "iPhones communicating to force reboots". I'm glad HN doesn't allow emoji, but I do wish I could add :facepalm: or :eye-roll: here.

JumpCrisscross 2y ago
Why? This seems like a smart anti-theft measure. (Bunch of iPhones in a radio silent environment together, maybe also not moving or detecting light.)
- kstrauser 2y ago
  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.
- Jtsummers 2y ago
  It's the faraday box part in particular. Airplane mode isn't a true no-radios mode on iPhone (this is well-known, or should be on HN at least). But it does leave cellular radios off. Wifi and bluetooth might need to be separately disabled and with wifi, at least, it'll turn back on after a while. So maybe (being very generous), if bluetooth or wifi is enabled or becomes re-enabled, there's a signal between the iPhones that causes this reboot behavior. But how is a device in a faraday box receiving this signal and rebooting? And why do they need a signal when they could just use their own clocks and determine that it's been X days or weeks since last going online and reboot?
  - JumpCrisscross 2y ago
    > how is a device in a faraday box receiving this signal and rebooting? Doesn’t need to. Being in a Faraday box is a reasonable trigger for a single reboot. That said, the most incredulous part of this story is that iPhones can detect when they’re in a Faraday cage.
    - Jtsummers 2y ago
      But the claim is that other iPhones in the area are triggering the reboot. Setting that claim aside, though, how would the device even tell it's in a faraday box versus just out in the woods?
      - JumpCrisscross 2y ago
        > the claim is that other iPhones in the area are triggering the reboot Lack of motion? The information the other phones provide are proximity (it’s unusual for people to pile their phones together), that the radios still work and possibly a timeline, e.g. if the other phone says “I’ve been in a suspicious state for two days,” the first phone can change its priors.
        LorenPechtel 2y ago
        I could easily see this as a security measure. Give the phone a concept of fear of being stolen. Phone, alone, continued source of power for an extended period. Somebody could have left it on a charger and gone away. Phone, continued source of power for an extended period and static bluetooth signals from other phones--what's going on here? This is very suspicious, turn defenses to max. It doesn't need to know the difference between thieves trying to thwart it and cops trying to thwart it.

JumpCrisscross 2y ago

Why? This seems like a smart anti-theft measure. (Bunch of iPhones in a radio silent environment together, maybe also not moving or detecting light.)

kstrauser 2y ago
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.
Jtsummers 2y ago
It's the faraday box part in particular. Airplane mode isn't a true no-radios mode on iPhone (this is well-known, or should be on HN at least). But it does leave cellular radios off. Wifi and bluetooth might need to be separately disabled and with wifi, at least, it'll turn back on after a while. So maybe (being very generous), if bluetooth or wifi is enabled or becomes re-enabled, there's a signal between the iPhones that causes this reboot behavior. But how is a device in a faraday box receiving this signal and rebooting? And why do they need a signal when they could just use their own clocks and determine that it's been X days or weeks since last going online and reboot?
- JumpCrisscross 2y ago
  > how is a device in a faraday box receiving this signal and rebooting? Doesn’t need to. Being in a Faraday box is a reasonable trigger for a single reboot. That said, the most incredulous part of this story is that iPhones can detect when they’re in a Faraday cage.
  - Jtsummers 2y ago
    But the claim is that other iPhones in the area are triggering the reboot. Setting that claim aside, though, how would the device even tell it's in a faraday box versus just out in the woods?
    - JumpCrisscross 2y ago
      > the claim is that other iPhones in the area are triggering the reboot Lack of motion? The information the other phones provide are proximity (it’s unusual for people to pile their phones together), that the radios still work and possibly a timeline, e.g. if the other phone says “I’ve been in a suspicious state for two days,” the first phone can change its priors.
      - LorenPechtel 2y ago
        I could easily see this as a security measure. Give the phone a concept of fear of being stolen. Phone, alone, continued source of power for an extended period. Somebody could have left it on a charger and gone away. Phone, continued source of power for an extended period and static bluetooth signals from other phones--what's going on here? This is very suspicious, turn defenses to max. It doesn't need to know the difference between thieves trying to thwart it and cops trying to thwart it.