In the 1987 case of California v. Greenwood, the U.S. Supreme Court ruled that law enforcement officers do not need a warrant to search and seize garbage left outside for collection in public areas. The case arose when police suspected Billy Greenwood was involved in drug trafficking and searched his trash bags without a warrant, finding evidence of narcotics use which led to his arrest. Greenwood argued this violated his Fourth Amendment rights against unreasonable searches and seizures. However, the court held that individuals do not have an expectation of privacy for discarded materials because they are readily accessible to animals, children, scavengers or snoops - thus no constitutional violation occurred with such searches by police officers.

In the dissenting opinion for California v. Greenwood, Justice Brennan, joined by Justice Marshall, argued that individuals have a reasonable expectation of privacy in their trash left out for collection on public streets. They contended that people expect their discarded items to be picked up and destroyed without inspection or intrusion into their personal lives. The majority's decision was seen as ignoring this reality and instead focusing on what they believed society should reasonably expect regarding privacy rights. The dissenters also pointed out the potential dangers of allowing warrantless searches of garbage bags - including possible misuse by law enforcement agencies and invasions into citizens' private lives - arguing these outweighed any benefits gained from such practices. They concluded that the Fourth Amendment should protect citizens against unreasonable searches like these unless there is clear evidence justifying an exception.