Radio Police Scanner Lite is a free app preconfigured with a list of emergency services radio frequencies, it can listen in to firefighters, ham radio, aircraft and live police radio, each feed comes from a person owning a police scanner in that geographical zone and sharing it via the Internet. Stations are classified by region and country with a built-in emergency services code to interpret what they are talking about, you can add any radio frequency broadcasted over the web in the RSS feeds link, it will automatically reconnect to the feed if it loses connection, favourites can be pinned to the front screen and accessible with a single tap.
There is only a delay of a couple of seconds in between the real talking and the broadcasting, you can browse the Internet while listening to a feed in the background, the only thing not guaranteed is that your country will be covered but the app is continuously expanding radio feeds, the paid for version of this app comes with thousands more of radio frequencies.
Many of the radio frequencies will be silent, the best way to spot what are the most active channels is by looking at the popularity of each feed, the more listeners the more likely it is that there is something going on or talking.
Investigation departments use encrypted radios to communicate during surveillance operations you won’t be able to listen to those, the radio will broadcast a routine police or firefighters working day. Police radio scanners are legal in many US states but is best that you check your local laws before using it as there are some restrictions like for example using a police scanner to impersonate a police officer, alternatively you can also listen to live emergency services online via your browser at Broadcastify.