The surveillance state is a pejorative term used to describe a national government's surveillance of large numbers of citizens and visitors. Such widespread surveillance is most usually justified as being necessary to prevent crime or terrorism.
The growth of state surveillance has led to concerns about the erosion of privacy and civil liberties, and also to worries that over-reliance on such measures may lead to complacency by law enforcement officers.
Examples of fully realised surveillance states are the Soviet Union, and the former East Germany, which had a large network of informers and an advanced technology base in computing & spy-camera technology. (Castells, M. The Rise of the Network Society, 2000)
But they did not have today's technologies for mass surveillance, such as the use of databases and pattern recognition software to cross-correlate information obtained by wire tapping, including speech recognition and telecommunications traffic analysis, monitoring of financial transactions, automatic number plate recognition, the tracking of the position of mobile telephones, and facial recognition systems and the like which recognise people by their appearance, gait, etc.
More recently, the United Kingdom is seen as a pioneer of mass surveillance. At the end of 2006 it was described by the Surveillance Studies Network as being 'the most surveilled country' among the industrialized Western states.
The ability to gather information about citizens is increased by mandating new checks on paper-based records, such as increased checking of employees' qualifications and CV's, and by the introduction of digitised biometric data in identity documents and their corresponding databases, and the cross-correlation of this data with DNA testing databases.
Some technological developments work in favour of the citizen rather than the state, especially communications software that uses strong encryption.
Many advanced nation-states have implemented laws that partially protect citizens from unwarranted intrusion - such as the Data Protection Act 1998 in the United Kingdom, and laws that require a formal warrant before invading someone's privacy.