Police officers do not need a warrant to seize contraband or evidence that is in plain view where the officer has a right to be. An officer’s seizure of an object in plain view does not violate the Fourth Amendment because the officer technically (and legally) has not conducted a search.
Example: During daylight hours, Officer Mendoza stops a car for having an expired license plate. When Officer Mendoza approaches the driver, the officer sees a packet of what appears to be illegal drugs on the front seat of the car. The officer seizes the packet and arrests the driver. The seizure was legal because the drugs were in plain view. Though the officer had no probable cause to search the car at the moment the officer pulled the car over, seeing the illegal drugs on the front seat gave the officer a valid basis for the seizure.
Example: Same case, except that the traffic stop occurs at night and Officer Mendoza sees the packet of drugs on the front seat only after shining a flashlight into the interior of the car. The seizure of the drugs is still legal. As long as police officers are standing where they have a right to be, objects that they see with the aid of a flashlight are in plain view.
Example: Officer Tanaka pulls a car over for running a red light. When the driver rolls down the window, Officer Tanaka detects a strong odor of marijuana emanating from inside the car. The officer orders the driver out of the car and conducts a search. Underneath the driver’s seat, the officer finds and seizes a pouch filled with marijuana. The seizure is legal. Smelling the marijuana gave Officer Tanaka probable cause to believe that the car contained illegal drugs (under what has come to be called the “plain smell” doctrine). The officer could therefore conduct an immediate search, without having to obtain a search warrant first.
However, a police officer can seize objects in plain view only if the officer has a legal right to be in the place from which the objects can be seen or smelled. If an officer has no legal right to be where the evidence or contraband is spotted, the plain view doctrine doesn’t apply. So, for example, if an officer illegally enters a house and observes contraband in plain view, his seizure of the item is not legal.