Is adding audio to surveillance cameras a threat?

The idea of adding security cameras with audio on public transportation is raising privacy concerns with the ACLU and others. In December the Washington Post and The Daily reported that the practice is spreading widely across the United States.
tiny cheap camera
It’s proposed that here would be six cameras per public bus and that would mean six microphones to pickup conversations. Recent events in several cities show the need for cameras and even body cameras for police. The size and cost of these cameras are dropping. Should we be concerned? Head more in this ACLU article.

May, 12, 2015