Knock-knock. Police officers are at your door, armed with a search warrant. But is that search warrant legally valid?
The Fourth Amendment protects your privacy by generally requiring police to get a valid search warrant before they can conduct a search of your home (or other places where you have a reasonable expectation of privacy). The warrant must be filed in good faith by an officer and be based on reliable information showing probable cause to search your premises.
There are, however, a few additional warrant requirements that you'll want to look for if presented with a search warrant. A warrant must include:
A magistrate's signature. After an officer applies for a warrant, a neutral and detached magistrate must issue the warrant and sign it. That means the magistrate must be impartial and outside of the "competitive enterprise" of law enforcement. For that reason, police officers and prosecutors generally can't serve as magistrates. State laws on magistrate qualifications vary widely; some states require that magistrates have an attorney's license, while others require only that magistrates be literate. If a proper magistrate never issued or signed the warrant, then the warrant (and the search) may not be valid.
A description of the place to be searched. The warrant must specifically state the place to be searched. For most residences, a street address usually satisfies this requirement -- unless the warrant designates an apartment complex, hotel, or other multiple-unit building, in which case the warrant must describe the specific sub-unit to be searched. This may seem like a given, but little mistakes can lead to innocent persons being ambushed by police in their own homes, as allegedly happened in one notable case reported by SF Weekly.
A description of the items to be seized. Finally, the warrant must specify "with particularity" which items are to be seized during the search. However, police may also seize contraband that isn't specified in the warrant (such as illicit drugs) if the contraband is in plain view of the officers performing the search.
So what if you challenge police over a questionable search warrant? While it may seem unfair, you can potentially be arrested for resisting a search -- though you can always file a claim afterwards alleging a violation of your rights. But keep in mind that police don't always need a warrant to conduct a search, so be sure to familiarize yourself with exceptions to the warrant requirement.