To monitor Police radio you could buy a police scanner, sit in front of a computer to listen to live streaming, or — thanks to developer Christopher Coudriet — US users can load the Police Radio application on their iPhone.
This US$1 app taps into internet streams of CB channels, which makes frequencies from all around the US available to users. It also comes at an obvious discount compared with the cost of a police scanner and the convenience of having a tool that travels.
The main screen on Police Radio is organised by state, each listing the channels available for streaming. Among the different emergency radio apps available via the App Store, Police Radio seems to have a lot of channels available; the developer also seems to be good about adding new frequencies by user request.
Selecting a channel will load up the stream with a list of scanner codes to help you decipher the chatter. If there is a stream you listen to online but isn't listed in the app, Police Radio also has the ability to play from a specific address, supporting most common feed types. If you would like to listen to a stream while doing other things on your device, there is also an option to play it in the background, which will launch a Safari stream.