Depends on what level do you trust. For me, I'd generally trust OS indicators. So, if iOS doesn't show me a mic on indicator when Facebook is not open I'll cons

Depends on what level do you trust. For me, I'd generally trust OS indicators. So, if iOS doesn't show me a mic on indicator when Facebook is not open I'll consider thar verification. A potentially better option would be if some independent non profit security firm audited major apps every once in a while, monitoring network traffic and such.