Final answer:
A search can be valid without a warrant or probable cause if it meets 'special needs' beyond regular law enforcement, such as border searches or in emergency situations ('exigent circumstances'). Probable cause is usually required for a warrant, but there are exceptions like the 'good faith' exception and the 'inevitable discovery' doctrine.
Step-by-step explanation:
A search is considered valid and without the necessity of a warrant or probable cause under certain special conditions, which are usually exceptions to the general rule requiring warrants. One of these exceptions is when the search meets 'special needs' beyond the normal purposes of law enforcement. These special needs might include, for example, searches at international borders or in schools for the purpose of maintaining a safe environment.
Probable cause is a legal standard that must be met before law enforcement can obtain a warrant for a search or arrest. It is the level of suspicion that would lead a reasonable person to believe that a crime has been committed or that evidence of a crime is present. While it is lower than the standard required for a conviction, it is still a necessary element for obtaining a warrant unless exceptions apply.
Searches may also be conducted without a warrant if there are exigent circumstances, such as a risk that evidence will be destroyed or tampered with before a warrant can be secured, or if the items to be seized are in plain view. Additionally, the 'good faith' exception and the 'inevitable discovery' doctrine are two other situations where evidence may be admissible even if the search that recovered it did not strictly adhere to legal requirements.