Yes. It is usually referred to as 'plain view.'
In general, police can search your trunk without a warrant or probable cause if they have your consent or if they believe there is evidence of a crime in the trunk.
To come into a home the police need a search warrant to search. Without the warrant the evidence is not admissible in court. It would be an illegal search.
A Search Warrant
Well, if the police department thinks that a cell phone may hold important evidence, then there is no need for a warrant. By the time the warrant is issued, the evidence may have been already destroyed or deleted.
Carroll Doctrine
They must provide a judge with probable cause to do a search.
No they can't. If they try to use it in court it would be immiscible.
Yes they can search it
Police obtain a search warrant by presenting evidence to a judge or magistrate that shows probable cause that a crime has been committed and that evidence related to the crime is likely to be found in the location to be searched. The judge then decides whether to issue the warrant, allowing the police to search the specified location.
The police need a Search Warrant to enter a private residence in order to collect evidence unless they have reasonable cause.
Yes, the officer may search. Police may search a building if they reasonably believe a valid search warrant has been issued. They do not have to possess the search warrant.
The police got a search warrent in order to search the suspect's house. The suspect would not allow the police to search his home without a search warrant.