Document Type


Publication Date



Since 1983, however, seven Supreme Court decisions have focused at least in part upon application of the Fourth Amendment to technological enhancement of, or technological substitution for, visual surveillance: United States v. Dunn and Texas v. Brown (artificial illumination); United States v. Knotts and United States v. Karo (electronic tracking devices); California v. Ciraolo9 and Florida v. Riley (aerial surveillance); and Dow Chemical Co. v. United States (image-magnifying aerial photography). Reaction to many of these decisions has been highly critical.

In six of the seven cases, investigators refrained from intruding physically into a location protected by the Fourth Amendment. The Supreme Court held in those cases that the surveillance was not a search. Only in Karo did investigators effect a kind of physical intrusion, and in that case the Court concluded that a search had occurred. This does not mean, however, that the Court has equated physical intrusions and searches in a simplistic manner. Particularly in those cases involving the use of sophisticated surveillance technology, the Court has proceeded cautiously, basing its decisions on narrow factual grounds, rather than taking the opportunity to enunciate or develop sweeping, general principles.

Still, certain patterns do emerge, or at least can be inferred, from this body of case law. In deciding whether technologically enhanced visual surveillance is a search, the Court, sometimes implicitly and sometimes explicitly, has considered three factors. Two relate directly to technology: the extent to which the equipment enhanced the officers' natural senses, and the availability of such equipment to the general public. The third factor that the Court has considered is the nature of the information sought or discovered by the surveillance. This Article analyzes these seven decisions. Part II provides an overview of basic Fourth Amendment principles. Part III reviews and critiques the Court's treatment of technology, specifically artificial illumination, the use of electronic tracking devices, aerial surveillance and image-magnifying technology. Part IV examines how the nature of the information sought and obtained by the surveillance has influenced the decisions at which the Court arrived. Finally, the Article summarizes and evaluates this case law.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.