There are times when searches can be performed without a court ordered search warrant. These are called warrantless searches and it's the most common type of search conducted by law enforcement.
The vital word in determining a warrantless search: Reasonable. It will be up to the court in many instances to determine if the warrantless search was reasonable. Really, this boils down to the court agreeing that law enforcement's judgment to search was based on logical criminal suspicion.
Consenting to searches
If you voluntarily allow police to search your home or car, this is called a consent search. This validates a search and, as a result, turns anything law enforcement finds into admissible evidence. Officers also do not have to tell people that they can decline thus granting law enforcement, without a warrant, the right to search the home.
One of the keys here is determining who has the right to consent to the search. If roommates live in a home, courts may say that the consent of a person to search the home does not apply to the personal areas of another in the same place. If there are separate bedrooms for instance, police could only search the one used the by the person who consented to the search.
Landlords and hotel managers cannot allow searches of leased areas. Company owners can consent to a search of the company, which can include work areas. But this search is limited from personal employee areas like a locker.
It will be up to prosecutors to prove consent was given in the proper manner.
The plain view doctrine
Just as it sounds. If a law enforcement officer can see evidence of criminal activity prior to entering or an initial search, then the officer is within their rights to enter without a search warrant. If an officer sees a weapon from a legal vantage point, he's allowed to proceed with a search. This is applicable to homes or cars.
The officer can't alter a normal vantage point to see possible contraband. The discovery of the evidence also needs to be unintentional. So, officers can't scale a tree to see in a window. They also need to come across evidence while already in a legal position outside or inside the home.
Police are allowed to search only the person arrested and the area where that person could acquire a weapon or could hide or destroy evidence following an arrest. And this search needs to happen during or immediately after arrest.
This allows the search to be consider "reasonable," because it is related to the arrest. Officers are allowed to use these searches as self-protection or to preserve evidence in connection with an arrest.
In other instances, warrantless searches are allowed in extreme circumstances. If the police feel someone's safety is at risk or criminal activity is occurring, and obtaining a warrant would increase those things, they can enter a home or vehicle and perform a search.
According to a law.com article, police received a 911 call about screaming in a New Jersey home. When they arrived, a man and his girlfriend said the noise was a result of sex. The officers asked the man for identification, which he went upstairs to retrieve. The officers went with him and saw loose marijuana and bagged marijuana. There were also marijuana plants in the house. All of this was discovered because of a combination of factors in warrantless searches. From the plain view Doctrine to entering the house to do a welfare check, police made an arrest without a warrant that stood up in court.
If someone is perceived to be in danger or police feel criminal activity is going on, they can enter using the emergency exception.
Searches of cars and their occupants
A recent 5-4 ruling by the Supreme Court has curtailed law enforcement's ability to perform a warrantless search of a vehicle.
If a person is cited for a traffic violation then detained in the back of a police car and poses no threat, police are not allowed to search the vehicle. Previously, warrantless car searches were allowed immediately following any arrest.
Warrantless searches can still happen if the passenger compartment was within reach of someone removed from the vehicle or if law enforcement thinks there is evidence in there. If a suspect had access to the vehicle during the time of the arrest, that also allows officers the right to check the vehicle.
Since warrantless searches are allowed in certain circumstances, people are almost always better off staying out of the way but making it clear they do not consent to the search. Remember, once in court the search will have to prove legal in order for evidence to be admissible at trial. Promptly contacting your attorney in any warrantless search situation is recommended.