The Fourth Amendment of the U.S. Constitution protects people against being
unlawfully searched or unjustly arrested by police. The text of the amendment
reads as follows:

“The right of the people to be secure in their persons, houses, papers, and
effects, against unreasonable searches and seizures, shall not be violated,
and no Warrants shall issue, but upon probable cause, supported by Oath
or affirmation, and particularly describing the place to be searched, and the
persons or things to be seized.”

Because of this amendment, police cannot conduct a search without probable
cause that the search will uncover evidence of wrongdoing. And they cannot
arrest you unless there is probable cause to believe you have committed a crime.

If you are searched without probable cause, any evidence collected must be
suppressed. This means it cannot be used against you in court. If you are arrested
without probable cause, the arrest is considered invalid and any evidence collected
as a result of it will be suppressed.

https://www.forbes.com/advisor/legal/criminal-defense/probable-cause/

Reasonable suspicion that a crime has been, is being, or will be committed is required.

No crime = no probable cause.

There are exceptions, such as exigent circumstances -- when failure to act could result in harm to others or destruction of evidence.  If there's enough suspicion to obtain a warrant, then you should force the cops to obtain a warrant before any searches.  More often, however, cops only threaten to come back with a warrant hoping you'll cooperate and agree to a search anyway.