Listening to police scanners has a long history in this country. If you're a journalist, a concerned citizen or just interested in hearing the chatter, you can tune in to emergency frequencies to stay on top of local events as they happen.
In the past, you needed expensive hardware and electronic equipment to listen to emergency bands. Now, all you need is a smartphone and one of these police scanner apps.
Before you use any of these apps, I encourage you to know your local laws regarding their use. While police scanners are legal in most states, some states restrict their use under certain conditions.
If you're in doubt about the legality of using these police scanner apps, consult with a professional lawyer. You can find one here.