Short answers, pulled from the story.
The court ruled that everyone has the right to be secure against unreasonable search or seizure, whether of the person, property, or correspondence. This principle appears in Article 14 of Italy's Constitution and Section 21 of the New Zealand Bill of Rights Act 1990.
By 2012, justices clarified that the reasonable expectation of privacy test had been added to but not substituted for the common-law trespassory test. Courts have found that individuals do not possess a reasonable expectation of privacy in information transferred to third parties, such as writing on the outside of an envelope sent through mail.
Police may follow a suspect into a residence during hot pursuit of a fleeing felon if probable cause exists. This exigent circumstances exception requires officers to act quickly because evidence is in imminent danger of being removed or destroyed.
Evidence obtained through illegal searches cannot be used against defendants at trial under the exclusionary rule. Some narrow exceptions exist when police acted in good faith pursuant to a warrant they believed valid at the time.
Justice Holmes ruled that general fishing expeditions into private papers violated the spirit and letter of the Fourth Amendment. Constructive searches involving corporate records do not apply the full Fourth Amendment since corporations lack certain individual rights.