Hi there! I'm the owner and operator of Broadcastify, which is the platform that powers all the apps that provide police scanners and public safety communications online. I'm an active HN reader and would be glad to answer any questions folks have. It's an interesting business to be in these days...
Isn't police radio usually scrambled? It is where I am in Norway. It was legal to listen to it before it was scrambled though. Not sure if it's legal to de-scramble it, if it's at all possible. AFAIK you can still listen to the ambulance channel, though, but sometimes the details are ... grisly.
In the United States, no. Police, emergency, first responder radio transmissions are generally in the clear. I don't know the precise history of it, but I have always assumed it is a combination of legacy (emergency radio in the United States is very old, and predates cheap and convenient electronic encryption standards), compatibility (first responder funding and maintenance in the United States is generally a local and state issue, so practices vary widely; for anybody to successfully come up with an encryption standard would require an unusual top-down standardization that has only been seen in extraordinary circumstances, such as after September 11th), and utility (in a disaster scenario where disparate groups coming from disparate points of the country might need to quickly ad hoc communications with each other, the absolute last thing you want is lives on the line while people are configuring their encryption protocols for their radios... Nor do you want to deny local volunteers the ability to understand where first responders are and how to get to them by having that information communicated in scramble).