In at least one state that I know of, it's illegal to have a scanner app on your phone if you are out and about. But it's OK for you to have the app if you're at home. I know, it doesn't make a whole lot of technological sense, but the idea behind the law is to make it illegal for criminals to listen to police communication while out committing a crime. So beware if you decide to install the app.

In practical terms, this is probably an extra charge they can slap on you if they get a probable cause to search your phone, but I am not a lawyer, as the famous internet adage says.

Now that I think about it, I confess my memory is a little shaky. For all you know, this may be outdated or incorrect information.