Source: https://www.schneier.com/blog/archives/2...

 In a study we conducted over a two year period in several US        metropolitan areas, we found that a significant fraction of        the "encrypted" P25 tactical radio traffic sent by federal law        enforcement surveillance operatives is actually sent in the        clear, in spite of their users' belief that they are        encrypted, and often reveals such sensitive data as the names        of informants in criminal investigations."I'd call that a negative externality.  Good thing no hostile powersoperate in our nation's capitol monitors and transcribe all of thisfor intelligence purposes and/or blackmail."