Department of Defense Regulation 5240.1-R, Procedures Governing the Activities of DOD Intelligence Components that Affect U.S. Persons, § C6.2.1 (Dec. 1982): “Concealed Monitoring”
Concealed monitoring means targeting by electronic, optical, or mechanical devices a particular person or a group of persons without their consent in a surreptitious and continuous manner. Monitoring is surreptitious when it is targeted in a manner designed to keep the subject of the monitoring unaware of it. Monitoring is continuous if it is conducted without interruption for a substantial period of time.