When the police knock on your door, you typically don't have to let them in unless they have a search warrant signed by a judge. But even if they do have a warrant, they can't act however they please.
A search warrant is a document signed by a judge that allows a police officer to search for specific items at a particular place and time. For example, a search warrant may authorize police search of "a single-family home located at 123 Main St." for "drugs and drug paraphernalia, packaging materials, scales, and other devices used for the preparation, sale, and administration of said drugs, any United States currency, and any weapons." Police can search only the place described in the warrant. For example, if they have a warrant to search your car, they can't also search your house.
Officers can seize any contraband or evidence of crime that they find while executing a warrant, even if the object isn't mentioned in the warrant. Officers can also take reasonable steps to protect themselves during a search, such as telling the occupants of the place to be searched to remain in a certain area and even handcuffing them. (For more information, see Search Warrants: What They Are and When They're Necessary.)
The knock-and-announce or knock-notice rule requires officers to announce their presence before entering a person's home. Generally, officers must knock on the door, announce their presence, and give the property owner a chance to open the door before entering. (Wilson v. Arkansas, 514 U.S. 927 (1995).)
But officers generally don't need to knock, announce, and wait if they:
And even when the police violate the knock-notice rule, courts often won't exclude the evidence they find.
Conducting a search in a reasonable manner generally includes showing the occupant of the home a copy of the warrant upon request. But if the occupant doesn't ask, the officer doesn't need to immediately display the warrant.
Courts generally frown on officers who fail to exercise even the most basic courtesy to cooperative people during the execution of search warrants. For example, officers aren't supposed to enter your home, refuse to show you the warrant, refuse to allow you to get dressed, then keep you outside in the hot sun for five hours without anything to eat or drink. Nonetheless, in one case, that's exactly what Alcohol, Tobacco, and Firearms (ATF) agents did to a woman when they executed a search warrant at her home. (U.S. v. Thompson, 667 F.Supp.2d 758 (S.D. Ohio 2009).)
People's homes are their castles, and the Fourth Amendment requires officers searching them to do so in a reasonable manner. If officers act unreasonably, a court may exclude evidence that they find. In the Thompson case, the court found that the officers acted unreasonably and threw out the evidence they found during the search.
If you are charged with a crime, talk to an experienced criminal defense attorney. An attorney can explain the law in your jurisdiction and protect your rights. If you aren't charged with a crime, but feel that officers violated your rights with an illegal or unreasonable search, you may want to talk to a civil rights or personal injury attorney about filing a complaint or a lawsuit.