I have a relative who is a cyber security expert. He is an “ethical hacker” for a major corporation. He leads a team that tries to break in to corporate data in order to strengthen their security. Recently I queried him about an incident where I discussed a health issue with my doctor and moments later was served up ads for dealing with that issue. My relative walked me through a few settings and told me that my phone was the likely culprit. Even though it was locked and in my pocket, the phone was listening for potential advertising. My relative told me that when he wants to have a truly private conversation with his fiancée, they put their phones in the microwave.
It occurs to me that it might be nice to make them a nice little box that would block RF and attenuate sound. So can I just buy some faraday cloth from Amazon and line the box? Are there any special tricks?