Abstract

This article addresses the question of whether an expectation of privacy is reasonable in the face of new technologies of surveillance, by developing a principle that best fits our intuitions. A "no sense enhancement" principle which would rule out searches using technologically sophisticated devices is rejected. The paper instead argues for the "mischance principle," which proscribes uses of technology that reveal what could not plausibly be discovered accidentally without the technology, subject to the proviso that searches that serve a great public good that clearly outweighs minimal intrusions upon privacy are permissible. Justifications of the principle are discussed, including reasons why we should use the principle and not rely solely on a utilitarian balancing test. The principle is applied to uses of aerial photography and heat-detection devices.