Or put the phone inside a Faraday Cage phone pouch.

Just because there is a physical control presented to the user doesn't mean there won't be any hidden connections inside the phone still.

I've tested two of those. It's hit and miss. If it's not closed perfectly flat (and it's metal-lined fabric, it's not always perfectly flat even if you're careful), it'll receive phone calls just fine.

A faraday cage works for incoming signals, but not so much for outgoing. It also depends on the wavelength vs size of mesh.

I think using a solid cage is the best bet.

Hi 'm463, you seem knowledgeable about this subject, so I have a few questions. Could you please answer the questions below or direct me to where I can learn more?

1. If a phone is off e.g. iOS’s General->Shut Down, then can it still receive and transmit signals?

2. What is the best kind of cheap case / enclosure for a cellphone that would prevent signals from being transmitted or received? Can I just wrap a cellphone in aluminum foil and place said wrapped cellphone in a Tupperware / plastic sandwich container?

3. What is an effective way for an RF layperson like myself to detect whether or not my phone is transmitting or receiving signals while it appears to be off e.g. RF tool or measurement device?

I just want a way to know and be completely certain that “off” means “off”.

Those are good questions and I'm not an expert. I was a part of a discussion once where someone mentioned that faraday cages mostly work for signals entering.

However:

1a) You don't know (because your phone can pretend to be off). You need to remove the battery (and also remove hidden batteries)

1b) some phones support NFC, which can theoretically be used when the phone is off.

2) I suggest being familiar with: https://en.wikipedia.org/wiki/Faraday_cage and your cellphone before making a decision

3) I don't know, but this would help with #2

there is the librem5 phone that has these physical switches

Also the Pinephone if i am not mistaken, though it will be a few more month till thats available.

Even the Librem 5 is on backorder, but at least I can find a price for the Lebrem 5 ($700)

The pinephone has a planed release price at 150. The dev-version currently available goes for the same amount.

If you can't trust a manufacturer to make software that does what you're told it does, what makes you trust the same manufacturer to make hardware that will physically disconnect?

Similar steps would have to be taken for monitoring the device to ensure the hardware switch does what it's told, same goes for the software.

We need the same for cameras and microphones, too.

Well, cameras just need you to block them.

Software blocks aren't good enough because a compromised system can lie and say something is blocked when it isn't. Hardware disconnects you don't need to worry about.

I think he meant put a physical cover over the lens.

You can still be fingerprinted based off the scratches on the lens.

https://www.insider.com/facebook-patent-photos-fingerprint-d...

If someone has hacked your computer such that they can control your camera, how worried are you about being fingerprinted?

I'm pretty sure I've seen similar attempts to identify a specific camera using things like sensor noise patterns and lens aberrations

Maybe, but more important, a potential hacker cannot see me nor my family anymore

that link is giving me a 404

You can't really put a cover over a microphone.

Nothing really helps when everyone is voluntarily buying always on surveillance tubes, headphones and glasses with Alexa/Google assistant that's always listening

I could imagine a mini-microphone playing continuous noise of the appropriate 'color' to mask everything.

Then turn off the speaker when you want to use the mic.

Or do what Snowden does and de-solder the microphone and rely on manually plugging in a mic in the headphone jack.

I considered doing that and using an external microphone, but I don't trust my skills to get everything back together in one piece. Even getting access to the board to do it seems to require the use of destructive force. I'd probably be perfectly fine with a phone that didn't include a mic and required an external one though. While I do use it to place and answer calls sometimes, it's almost exclusively used for texting, and I haven't run into an occasion where loss of audio while recording video would matter.