Surveillance is the monitoring of the behavior, activities, or other changing information, usually of people for the purpose of influencing, managing, directing, or protecting them.
Behavior is the range of actions and mannerisms made by individuals, organisms, systems, or artificial entities in conjunction with themselves or their environment, which includes the other systems or organisms around as well as the physical environment.
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This can include observation from a distance by means of electronic equipment, or interception of electronically transmitted information ; and it can include simple, relatively no- or low-technology methods such as human intelligence agents and postal interception.
Postal interception is the act of retrieving another person's mail for the purpose of ensuring that the mail is not delivered to the recipient, or to spy on them.
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The word surveillance comes from a French phrase for "watching over", and is in contrast to more recent developments such as sousveillance.
Sousveillance is the recording of an activity by a participant in the activity, typically by way of small wearable or portable personal technologies.
Surveillance is used by governments for intelligence gathering, the prevention of crime, the protection of a process, person, group or object, or for the investigation of crime.
It is also used by criminal organizations to plan and commit crimes such as robbery and kidnapping, by businesses to gather intelligence, and by private investigators.
A private investigator, a private detective, or inquiry agent, is a person who can be hired by individuals or groups to undertake investigatory law services.
Surveillance is often a violation of privacy, and is opposed by various civil liberties groups and activists.
Civil liberties or personal freedoms are personal guarantees and freedoms that the government cannot abridge, either by law or by judicial interpretation, without due process.
Privacy is the ability of an individual or group to seclude themselves, or information about themselves, and thereby express themselves selectively.
Liberal democracies have laws which restrict domestic government and private use of surveillance, usually limiting it to circumstances where public safety is at risk.
Authoritarian government seldom have any domestic restrictions; and international espionage is common among all types of countries.
Espionage is the obtaining of information considered secret or confidential without the permission of the holder of the information.
Authoritarianism is a form of government characterized by strong central power and limited political freedoms.