The definitive literary treatment of a police state is George Orwell's novel Nineteen Eighty-Four, which describes a totalitarian regime that uses the excuse of constant war to permit police and security cameras to surveil the entire population.
Until the fall of the Berlin Wall, a classic modern police state was East Germany, or the German Democratic Republic (GDR). The country's secret police force, the Stasi (or Ministerium für Staatssicherheit) maintained an incredibly close watch over East German citizens, to the point where virtually every residential building, place of employment or place of leisure was home to at least one Stasi informant.
The constitution of the United States has provisions in place to protect citizens from unreasonable actions by police. Specifically, the U.S. Constitution and the Bill of Rights assert that people accused of crimes have certain rights, such as
However, many attempts have been made to bend these rules and regulations throughout the history of the United States. Recently, reaction to the September 11, 2001 Terrorist Attack, and the passage of the USA PATRIOT Act has expanded powers of the government to surveil and detain people it considers potential terrorists without affording them rights of due process, such as those listed in the Fourth, Fifth, and Sixth Amendments. A proposed new act, the Domestic Security Enhancement Act of 2003 is likely to accelerate this process, and is being fought by civil libertarian groups like the ACLU.