We as a developer community, and more generally as citizens, need to propose a new law in each state that specifically allows the law to catch up to recent technology by explicitly allowing these apps, their streams, and the developers to listen (not broadcast) to any public service employee radio communication (police, fire, ems, utilities, FBI, etc etc).
Why?
Who will watch the watchers? If watching is limited to antiquated mechanisms, then it isn't really watching.
I will be contacting my state rep / sen to introduce such legislation, since I also intend to develop apps for mobile use (none of mine are related to this story... but who knows what can be wrapped up under a zealous prosecution / DA).
Don't be afraid of legislation-eese and legal speak. It is just a syntax. There are rules for form of the law. Laws are just specifications.
Take affirmative steps to both protect developers from prosecution due to illegal use of their app, and to protect citizens so they can effectively watch their public officers.