[Jeffhs]

I think one big reason police and fire departments went from VHF to UHF, digital, etc. was to prevent folks outside the departments from listening in. These signals, after all, are not meant to be listened to by the general public; the police, fire departments and such won't make a fuss about it as long as you don't repeat what you hear over their frequencies, but still these are not supposed to be overheard by unauthorized persons. The fact that they are radio signals easily heard via standard receivers makes no difference. I believe this was even the case in the 1930s, when police departments had "one-way" radio systems that operated above 1700 kHz. The officer(s) would receive the call from the dispatcher over the car radio, then would call in to the precinct using police "call boxes" connected directly to police HQ and mounted on telephone poles. Many home radios of the '30s could tune in these one-way signals at 1700-1710 kHz (they would receive only the officer's end of the transmission), but, then as now, the signals were not meant to be overheard. The nature of radio signals makes it impossible not to hear these transmissions if you have the proper receiving equipment and know where to listen; however, if police and fire departments are really intent on making their transmissions private, they can and will do everything in their power (and budget) to do so, including moving to higher frequencies, digitally scrambling the information carried over said frequencies, and so on.

These days, with the Internet and chat, VoIP, etc. it would not surprise me if many police departments are abandoning traditional radio systems altogether, using chat and other modern-day communications techniques to communicate with headquarters and between officers. This may reduce the chances of ordinary people eavesdropping on the police/fire departments, but it won't stop it in any event. The only way to completely end all eavesdropping will be if someone eventually invents a method by which chat and VoIP communications between and among public-service agencies such as police and fire departments can be scrambled in such a way that people not meant to hear them cannot do so, using ordinary computers.