What about a Faraday bag?

A faraday bag works (but be sure to test it).

Be aware, though, that phones will increase their radio power and retry constantly when they aren't reaching a cell tower. If the increased battery drain is an issue, put your phone in airplane mode first.

That is a great option.

anyone have any suggestions for a Faraday bag?

Two bags of chips. With or without the chips.

https://usa.kaspersky.com/blog/terminator-dark-fate-chips/18...

Wrapping it in aluminum foil works, too.

Anything that completely surrounds the phone with conductive material will do the job.

theoretically the phone could still record all audio and then sync with the cloud when back online, but I'm grasping at straws here.

In such case the solution is to have hardware kill switches, like on my Librem 5.

That kind of phone goes so far to protect your privacy it won't even let you use it to call anyone. (https://www.techrepublic.com/article/librem-5-review-the-lin...). The real solution is regulation with lots of teeth and oversight, so we don't have to depend on flawed products that don't work.

This is an extremely old review, when the software was in beta. Phone calls are working fine for me now.

Regulations are great, but I prefer to have both kinds of defense.

That's a good sign! I'd given up all hope for the Librem and pinephone. I guess it's time to take another look...

I agree that hardware switches are ideal, but I don't see them being common since most of the folks pushing out phones want to use those devices to collect data on the people who buy them.

Why would it, though? If you're the sort who puts your phone into a faraday cage, you're not the sort who will install an app from the stores.

zero day OS-level exploit by some govt? idk.

I thought we were talking about retail stores here, not governments.

If your threat model is governmental, then that's a whole different thing entirely. You'll have to go to true extremes to even have a chance at defending against that. For instance, you shouldn't have a cell phone at all.

Airplane mode has to be able to make it zero-emissions due to FAA regulations, right?

The FAA no longer prohibits this stuff, although the airlines still have their own restrictions.

The FAA also only ever had rulemaking about BT and WiFi, because the use of the cell transmitter in flight is prohibited by the FCC, not the FAA. I don't know what the FCC's rules are, precisely.

I am going to the grocery store, not blowing up a pipeline. I doubt Kroger is going to remotely activate my baseband modem. Even if they did, I have an anonymous phone with a burner SIM.