Warrantless surveillance is the collection of information that people might reasonably assume to be private without a warrant from a judge approving the activity. Surveillance in general is a very broad term that can describe everything from observing people in public to intercepting private communications. As a general rule, surveillance without a warrant is legal if it takes place in a public environment. Warrants are required, however, when surveillance involves a breach of privacy.
Most commonly, warrantless surveillance involves intercepting communications. This includes phone calls, text messages, and Internet communications. It can also involve placing bugs and other monitoring devices in an area where people might believe that they are in private, such as the boardroom of a corporation.
In the 2000s, warrantless surveillance became a hot news item in the United States when a series of lawsuits revealed that the National Security Administration (NSA) had engaged in an extensive warrantless surveillance program as part of the War on Terror. Some of this surveillance was conducted with the willing assistance of telecommunications companies, which caused considerable outrage among consumers. Some customers of companies that turned over communications and other records that usually need a warrant were horrified to learn about the cooperation of their communications utilities in the program.
The government's justification for warrantless surveillance is that it is sometimes necessary to start surveillance immediately, without waiting for a warrant, and that being forced to wait might result in missing valuable and important information. Furthermore, obtaining a warrant can provide notification, which would alert people to be on their guard and thus defeat the point of the surveillance. Being able to conduct surveillance without a warrant, in other words, would provide flexibility and would be more likely to result in usable information.
Opponents of warrantless surveillance believe that it is a breach of privacy. People may exchange a variety of information via communication methods that they believe to be private and some people believe that citizens have a right to privacy in their communications. In countries like the United States with a long history of aggressively defending privacy rights, the thought of infringement upon privacy is especially repugnant to some citizens.
The legality of warrantless surveillance varies. In some regions, it is simply illegal in any form. In others, it can be used to gather information, but that information must be verified by other means; recordings of an illegal wiretap, for example, cannot be used in court as evidence. Other nations allow information gathered with warrantless surveillance into evidence.