What grounds do law enforcement use to put you on servalance?

Law enforcement can place individuals under surveillance based on reasonable suspicion or probable cause that the person is involved in criminal activity. This may include evidence of prior offenses, suspicious behavior, or credible tips from informants. Additionally, surveillance can be justified in cases involving serious crimes, threats to public safety, or ongoing investigations. Legal standards, such as obtaining warrants, may also apply depending on the type and extent of surveillance.