Exception #1: Search Incident to Lawful Arrest
Under Arizona v Gant, police are permitted to conduct a warrantless search of the person, and the immediate surroundings of the person, to seek out dangerous weapons, or evidence that may otherwise be destroyed. Cases hold that where the arrest is determined to be unlawful, so too, will be the seizure of evidence.
Exception #2: Plain View Exception
As long as police have a right to be where they were, when they saw evidence of a crime in plain view, there is no requirement that a search warrant be obtained. Washington v Chrisman is an example of a case in which the seizure of evidence in plain view, was upheld, despite there being no warrant. A notable example of a "plain view" evidence seizure is where the police rummage around through your garbage; yes, they sometimes do that, because no, we have no expectation of privacy in trash put out to the curb. That's what the US Supreme Court held in California v Greenwood.
Exception #3: Consent to Search
If a person with proper authority consents to a search, they will not be heard to complain about it, in the event evidence is obtained. If that consent is found to be obtained deceptively, the court may hold the evidence to have been taken without consent, and it may be “suppressed”. However, the US Supreme Court held in Schneckloth v Bustamante, that knowledge of a right to refuse the police consent to search is a factor to be taken into account, the Prosecutor does not need to prove that the one giving permission to search knows that he/she has a right to withhold that consent.
Exception #4: Stop & Frisk
We already reviewed this above, in connection with “stops”. If the police find probable cause, during a lower-standard “reasonable suspicion” stop, no court in America is going to require them to get a warrant. This was the basis of the Terry decision cited above, and it is often the basis on which serious/infamous/”most wanted” criminals are stopped; you may recall that Timothy McVeigh was stopped after the Oklahoma City bombing, based on a busted tail light.
Exception #5: Automobile Exception
The US Supreme Court has held as early as 1925, that due to the inherent mobility of automobiles, and the potential loss of evidence, police are given significant leeway to search autos, before warrants are required. The officer must have probable cause to believe that the vehicle (which could be a boat, not just an auto), contains evidence of a crime, fruits of a crime, etc. This nearly century-old rule, remains the law to the present day.
Exception #6: Hot Pursuit
As the name implies, where law enforcement personnel must move quickly to prevent the escape of a criminal, or the destruction of evidence, the law will allow seizures of evidence, and arrests of persons, without warrant. US v Santana, is an example.
Exception #7: Exigent Circumstances
Where there is a reasonable fear that people may be in danger, evidence may be destroyed, or a suspect may escape, police are given significant leeway to seize evidence and persons without a search warrant.
In Missouri v. McNeely, the Supreme Court clarified, "A variety of circumstances may give rise to an exigency sufficient to justify a warrantless search, including law enforcement's need to provide emergency assistance to an occupant of a home . . . engage in “hot pursuit” of a fleeing suspect . . . or enter a burning building to put out a fire and investigate its cause." Courts will typically look at the time when the officer makes the warrantless search or seizure to evaluate whether at that point in time a reasonable officer at the scene would believe it is urgent to act and impractical to secure a warrant. Courts may also consider whether the facts suggested that the suspect was armed and planning to escape, whether a reasonable police officer would believe his safety or others’ safety was threatened, and whether there was a serious crime involved.
Exception #8: Inevitable Discovery
This "exception" is really one that swallows the rule, and shows just how biased courts have become, against persons charged with crimes. Under the "inevitable discovery" exception, courts have held that evidence that would have been discovered inevitably, can be admissible, even without a search warrant. Nix v Williams is an example.
Exception #9: Health/Safety of Suspect
Where the police are actually trying to render aid to the person they wind up suspecting of illegal activity. The Michigan case of People v Brzezinski is an example.
Exception #10: Inventory Search
Where a suspect is arrested, his/her property is inventoried, with the ostensible purpose of making sure the property is returned, once the suspect is released. In Michigan, this is applied so expansively, that this has become another exception, which swallows up the rule; the cases hold that the police agency must have a written, definite policy on inventory searches. Examples of inventory search cases include Florida v Wells, and South Dakota v Opperman