Years ago it was an amusing pastime for many people to keep a radio tuned to the local police or fire department frequencies, listening in on the occasional highly charged conversations about a bank robbery in progress, an office building on fire, or a high-speed chase as the event unfolded. The radio frequencies used by law enforcement agencies and fire departments used to be available in books at the corner bookstore; today they're provided in listings on the Web, and from a book you can buy at Radio Shack—frequencies for local, county, state, and, in some cases, even federal agencies.