Weeks marked the advent of the Exclusionary Rule, under which evidence seized illegally is barred from court. Prior to this decision, the assumption had been that the needs of justice outweighed the rights of persons whose property had been illegally taken as evidence.

Weeks was tried and convicted on federal charges of sending lottery tickets through the mails. During his trial, he demanded the return of his personal effects, which had been seized as evidence during warrantless searches by state officers and a federal marshal, and their exclusion as evidence in the trial.

When the court refused, Weeks took the case to the Supreme Court on the basis that use of illegal evidence violated his rights under the Fourth and Fifth Amendments which, together, protect against illegal government encroachment on private property and personal liberty.

Writing for the unanimous Court, Justice William R. Day relied exclusively on the Fourth Amendment to reverse the lower court's judgement. He pointed out the importance of the federal courts' obliging the protections of liberty and property afforded by the Amendment against unlawful intrusions, and felt that the warrantless searches, and the refusal to return property gained in them, violated Weeks' constitutional rights.

Although the Weeks decision marked the formal adoption of the Exclusionary Rule first suggested in Boyd v. U.S. (1886), it did not incorporate the Fourth Amendment into the Fourteenth, making it active against the states. That occurred forty-five years later in Mapp v. Ohio.

During Prohibition, beginning just six years after this decision, the Court applied much looser standards to its view of the Fourth Amendment, allowing such conveniences as warrantless vehicle searches. Much later, in recent decades the Court has excluded a variety of fine points from the warrant requirement, including aerial police surveillance, searches of privately owned open fields and garbage bins, and arrests based upon anonymous tips that accurately reflect the behavior of a suspect.

The fact that those who rely most on the Fourth's protections often seem to be those with the most to hide, has tended to relegate the Amendment to secondary status in the pantheon of personal rights. But we need to remember Justice Louis Brandeis' timeless interpretation that the guarantees contained in the Fourth "conferred, as against the government, the right to be let alone -- the most comprehensive of rights and the right most valued by civilized men."