In an 1886 case, the Supreme Court defined "curtilage" as "the area to which extends the intimate activity associated with the sanctity of a man’s home and the privacies of life." (Boyd v. U.S.) In many cases, the curtilage will include the yard, garage or carport, and smaller structures surrounding the home. The entire residential area—including both the home and the curtilage—has the same heightened protection of privacy under the Fourth Amendment. (Oliver v. U.S.) However, even within the curtilage, police may generally go wherever the mailman, deliveryman, or other members of the public are impliedly invited, such as walkways and front doorsteps. (U.S. v. Robbins)
There are no hard and fast rules as to what constitutes "curtilage," but in U.S. v. Dunn, the Supreme Court listed four factors that lower courts must consider in deciding whether certain areas or structures are within the curtilage:
1. How close is the area or structure to the home, or how far away? Nearby structures or areas are more likely to be within the curtilage; remote structures or areas are less likely to be.
2. Is there a common wall or fence enclosing both the home and the area claimed to be curtilage? Areas and structures inside the residential fence or wall are more likely within the curtilage.
3. What appears to be the primary use of the structure or area? Something closely connected to family and household activities is more likely part of the curtilage; commercial or secondary uses tend against such a finding.