You are protected from illegal searches and seizures by the Fourth Amendment to the U.S. Constitution. You have an expectation of privacy on your own private property.
What this means is that you do not have to submit to a search of that property, even if the police ask for your consent. Many people feel that they need to do whatever the police ask or that they cannot say no, but this is not actually the case. You can refuse to give consent, and that is when police officers would need to return with a search warrant.
How do they get a search warrant?
In order to obtain a warrant, officers must go to a judge. An officer cannot issue a search warrant themselves, but must demonstrate probable cause and show that there is a valid reason to search your property. The judge will then give them a search warrant stipulating where they can search, what type of evidence they can look for and when they are allowed to execute the warrant.
What if it is an emergency?
There are rare exceptions to this rule, usually involving emergency situations. The police could be in hot pursuit of a suspect, they could believe that the public is in danger or they may believe that the evidence they are searching for is being destroyed on your property at that very moment. But even if they use an emergency as an excuse to execute a search without a warrant, they do have to demonstrate after the fact that it was a valid emergency.
Legal defense options
Do you believe that the police may have conducted an illegal search of your home? This can have a major impact on your case and the evidence that can be used, so it is important to carefully look into your legal defense options.

