A more thorough explanation:

The knock-and-announce rule is a legal principle that requires police officers to knock and announce their presence before entering a residence to execute a search warrant. This means that the officer must knock on the door, identify themselves as a police officer, state their purpose for being there, and wait a reasonable amount of time for the occupants to let them in.

For example, if a police officer has a search warrant to search a suspect's home for drugs, they must knock on the door, say "Police, we have a search warrant for drugs," and wait for a reasonable amount of time for the suspect to answer the door before entering.

If a lawsuit is filed over an officer's entry into a home, a court will determine whether the entry was reasonable. The court will consider whether the officer followed the knock-and-announce principle, among other factors.

However, there are situations where officers are not required to knock and announce their presence. For instance, if officers suspect that announcing their presence would be dangerous, futile, or result in the destruction of evidence, they may enter the residence without knocking and announcing.

It's important to note that violating the knock-and-announce rule does not necessarily mean that evidence obtained during the search will be excluded from court proceedings. In 2006, the Supreme Court ruled in Hudson v. Michigan that the violation of the knock-and-announce rule does not justify excluding evidence related to the violation of this rule.