A more thorough explanation:

Warrantless means that government officers carry out a search or arrest without a warrant or any other legal authorization. This means that they do not have permission from a judge to search or arrest someone. The requirement of a warrant serves to protect individuals’ privacy interests against unreasonable governmental intrusion. Evidence obtained without a warrant is per se unreasonably seized and should be excluded unless it falls under the exceptions that permit a warrantless search and arrest.

• Plain View Doctrine: If an officer is lawfully on the premises or stops the vehicle for a lawful purpose, and “the incriminating character of the item is immediately apparent,” the officers can seize that in plain view, even if it is not on the warrant list.
• Exigent Circumstances: Officers will take immediate actions to secure a warrant or they may search warrantless if they believe that failing to do so will cause the destruction of evidence, threaten public safety, or cause a suspect to flee.
• Consent: A third party with possessory rights of the property may have authority to consent to a search if consent is voluntarily given.
• Automobiles: If the officer has probable cause to believe that an automobile contains evidence of a crime or contraband, they can search automobiles, including the trunk and luggage, or other containers which may reasonably contain evidence or contraband, without a warrant.
• Stop and frisk: If officers have reasonable suspicion that a crime is occurring, they can stop a suspect for weapons to ensure their safety.
• Arrest: A search incident leading to an arrest may not require a warrant. If the officer just searches a suspect’s immediate surroundings to prevent destruction of evidence or secure safety of themselves or nearby people.

For example, if a police officer pulls over a car for speeding and sees a gun on the passenger seat, they can seize the gun without a warrant because it is in plain view. Another example is if a police officer is chasing a suspect and the suspect runs into a house, the officer can enter the house without a warrant to prevent the suspect from escaping.

These exceptions are important because they allow law enforcement to act quickly in situations where waiting for a warrant could result in harm to the public or the destruction of evidence. However, they must still follow the Fourth Amendment and ensure that their actions are reasonable and justified.