A police state is a political condition where the government maintains strict control over society, particularly through suspension of civil rights and often with the use of a force of secret police. This implies that the control by the government contradicts the will of the people being controlled. Thus, a police state is inherently anti-democratic. It is similar to martial law.
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