Do citizens have any Fourth Amendment protection from senseenhancing surveillance technologies in public? This Article engages a timely question as new surveillance technologies have redefined expectations of privacy in public spaces. It proposes a new theory of Fourth Amendment security based on the ancient theory of curtilage protection for private property. Curtilage has long been understood as a legal fiction that expands the protection of the home beyond the formal structures of the house. Based on custom and law protecting against both nosy neighbors and the government, curtilage was defined by the actions the property owner took to signal a protected space. In simple terms, by building a wall around one’s house, the property owner marked out an area of private control. So, too, the theory of personal curtilage turns on persons being able to control the protected areas of their lives in public by similarly signifying that an area is meant to be secure from others.

This Article develops a theory of personal curtilage built on four overlapping foundational principles. First, persons can build a constitutionally protected space secure from governmental surveillance in public. Second, to claim this space as secure from governmental surveillance, the person must affirmatively mark that space in some symbolic manner. Third, these spaces must be related to areas of personal autonomy or intimate connection, be it personal, familial, or associational. Fourth, these contested spaces—like traditional curtilage—will be evaluated by objectively balancing these factors to determine if a Fourth Amendment search has occurred. Adapting the framework of traditional trespass, an intrusion by sense-enhancing technologies into this protected personal curtilage would be a search for Fourth Amendment purposes. The Article concludes that the theory of personal curtilage improves and clarifies the existing Fourth Amendment doctrine and offers a new framework for future cases. It also highlights the need for a new vision of trespass to address omnipresent sense-enhancing surveillance technologies.