If the warrant specifies a certain person to be searched, the police can search only that person, unless they have independent probable cause to search other persons who happen to be present at the scene of a search. If an officer merely has a reasonable suspicion that an onlooker is engaged in criminal activity, the officer can only question the onlooker and, if necessary for the officer's safety, conduct a frisk for weapons (but not do a full search).

When Search Warrants Aren't Required

Most searches occur without warrants being issued. Over the years, the courts have defined a number of situations in which a search warrant is not necessary, either because the search is per se reasonable under the circumstances or because, due to a lack of a reasonable expectation of privacy, the Fourth Amendment doesn't apply at all.

Consent Searches

If the person in control of the premises freely and voluntarily agrees to the search, the search is valid and whatever the officers find is admissible in evidence. Police officers do not have to warn people that they have a right to refuse consent to a search. If a police officer wrangles a consent through trickery or coercion, the consent does not validate the search.

Many disputes about consent have to do with who has the right to consent. If there are two or more separate tenants in one dwelling, courts often rule that one tenant has no power to consent to a search of the areas exclusively controlled by the other tenants (for instance, their separate bedrooms). Similarly, a landlord lacks authority to consent to a search of leased premises. The same is true for hotel operators. On the other hand, an employer can validly consent to a search of company premises, which extends to an employee's work area but not to clearly private areas such as an employee's clothes locker. A tricky twist is that the consent in these types of cases will be considered valid if the police reasonably believe that the consenting person has the authority to consent, even if it turns out they don't.