The guiding rule about PRIVACY, in most western democracies is the phrase "expectation of privacy."
If you expect privacy while handcuffed in the back seat of a police car and you are talking to your buddy who is also handcuffed, you should have no expectation of privacy.
Urban areas are installing cameras and sound equipment because the GREATER PUBLIC GOOD of stopping speeding through traffic lights, terroristic threats on a city sidewalk WILL TRUMP youR right to PRIVACY.