Microphone and camera data sounds like a bit of a stretch to me. The data storage and network throughput required to do such a thing on a large scale would be astronomical, not to mention it would be easily exposed. I think the well-known monitoring of call records and text messages and ubiquity of cloud storage for photos combined with ease of obtaining warrants and buying information more than suffices for government or large corp use, and if they do monitor mics and cameras that would be using a targeted approach.
You could always try buying a mobile base station and setting up a lab to analyze everything your phone is transmitting. I'm sure people have done similar experiments before.
https://en.wikipedia.org/wiki/Magic_Lantern_(software)
https://en.wikipedia.org/wiki/Carnivore_(software)
It is what Edward Snowden tried to warn us about that turned him from a hacker to a criminal.https://theintercept.com/2014/03/12/nsa-plans-infect-million...
Not only that this website tells you the OSes to use and apps to avoid being spied on by the NSA: https://prism-break.org/en/
By isolating the memory the baseband processor can access, it's possible to limit the impact of its compromise. So of course it's nearly impossible for a consumer to figure out which phones do this isolation.
Of course, he might have just been bullshitting me.
This second OS performs very few operations, such as recording and sending data to the network over time when it's connected to the internet. Or it doesn't even need an internet connection. It sends the information every six months, so you don't even feel it. The data is collected in a very lightweight, encrypted, zipped, alien technology way, so it's inconspicuous.
I don't think this is a viable argument because we have no baselines here. In case phones have been running a shadow OS for many years now across the board there just are no phones around to compare battery usages in a meaningful way. "Drain very badly" isn't a figure I can measure when all phones do the same. All the older phones that run through my hands have generally a "bad" battery life cycle; I ascribe that to battery degradation plus technological advancements that have raised the bar.
Though they are also plugged in to the technology stack for yet other reasons.
It's one thing to have an idea ("Oh I know my phone could be eavesdropping on me"), another to estimate its plausibility ("But that could never happen, unless—aliens!"), and yet another to find evidence ("We were able to identify on-chip circuitry that structurally amounts to a CPU-in-a-CPU", "We were able to intercept signals from the device that cannot be explained by regular usage and would appear to have been initiated by the device without user action").
That's a slippery road indeed when the manifestation of a thought in one's brain is enough to convince one of the reality of it. I have to deal with people who suffer from this, and just as an aside, it often seems to be connected to outlandish claims; in the matter discussed here, that's happening when OP writes "Microphones and cameras may sound like a stretch, unless it's a super top-secret alien technology that hasn't been publicly revealed". Not even sure "alien" here is to mean "extra-terrestrial" or just "outlandish", but at any rate I sure can make any narrative sound plausible by introducing an improbable factor. Fairy tales work that way.
As for the assumption of "alien" tech that enables clandestine transmission of (useful, therefore voluminous) video data, there are mathematical boundaries here that we can use as guardrails for sanity: even not-yet-public and / or alien tech has to abide by the laws of physics and mathematics. For the narrator of a fairy tale, that is not a problem, of course: "But what if they use undetectable carrier waves? X-Waves??" OMG we're DOOMed.
If the pandemic has taught me something it is that some people come with a veneer of "critical", "independent" thinking, only to then, under the pressure of lockdowns, turn out to be someone who doubts everything related to vaccines ("it's not natural", "vaccines actually cause polio") while readily believing any kind of striped BS they heard somewhere on the internet or from an acquaintance. Any kind of striped BS.