Right, but if it’s compromised what’s a faraday cage going to do? As soon as you remove it from the cage it’ll reveal your location.

Here’s a pdf link to a 2020 NSA publication on the subject: https://media.defense.gov/2020/Aug/04/2002469874/-1/-1/0/CSI_LIMITING_LOCATION_DATA_EXPOSURE_FINAL.PDF

It seems that powering the device off is sufficient unless the device is compromised.

Some phones, even if they are turned off, still send telemetry data.

I can’t find anything other than redditors making this claim. Is there a better source I can look into?

Why would one want to put their phone in a faraday cage? I know what the cage does, but don’t understand why you’d want to use one instead of turning the device off.