Jailbreaks through the web are always a threat - they don't stop being a threat because you're using a legit cell tower. So I think that "what if there's a low-

Jailbreaks through the web are always a threat - they don't stop being a threat because you're using a legit cell tower. So I think that "what if there's a low-interaction 0-day" doesn't really interact with Stingrays. If you're worried about it, avoiding events where Stingrays are likely to be used doesn't really help you. iOS does verify OS software via a secure-boot-style chain of trust, starting with a public key that's part of ROM, and there's rollback prevention for the OS, the baseband, and the Secure Enclave's software. https://www.apple.com/business/docs/iOS_Security_Guide.pdf https://www.apple.com/business/docs/iOS_Security_Guide.pdf (At least, if you believe Apple, and if you don't, stop putting interesting info on your Apple cell phone.) Android also does verified boot https://source.android.com/security/verifiedboot/verified-boot https://source.android.com/security/verifiedboot/verified-bo... but device support is probably all over the place. I think that anything running Android 6 or later is required to use ARM TrustZone, but it's probably a lot easier to defeat than iOS's mechanism. Rupprecht et al. 2016 find that most devices on the market at the time - including the iPhone 5S and 6S and the Nexus 5 and 7 - would accept the LTE no-encryption mode ("EEA0") without showing any UI warning or indicator; see section 5 / table 2 in https://www.usenix.org/system/files/conference/woot16/woot16-paper-rupprecht.pdf https://www.usenix.org/system/files/conference/woot16/woot16... . They also find that some Huawei chipsets will accept the LTE no-integrity-protection mode ("EIA0"), although most devices reject that. I haven't seen a newer version of this research. NIST points out (https://csrc.nist.gov/CSRC/media/Presentations/LTE-Security-How-Good-is-it/images-media/day2_research_200-250.pdf https://csrc.nist.gov/CSRC/media/Presentations/LTE-Security-... slides 40 and 47 - warning, 3-megabyte PDF) that most phones support downgrading to older standards - which is what you want for roaming, but if you're in a densely populated area with a clear view of the sky and your phone shows "3G", maybe you should be suspicious. Your 75-year-old uncle with a thrift store Android is almost certainly at serious risk, yes, but I think his primary problem is that this Android isn't getting updates any more and there are just publicly known exploits that anyone can use. Personally, I'd say the best thing is to get him a ~$150 iPhone SE from one of the prepaid carriers, because that's what they're going for these days, the SE should have about two more years of security support lifecycle left, and it does have a Secure Enclave.