No Knock Warrant - In the US, a no knock warrant is a warrant issued by a judge that allows law enforcement officers to enter a property without knocking and without identifying themselves as police. It is issued under the belief that any evidence they hope to find can be destroyed during the time that police identify themselves and the time they secure the area.
Federal judges and magistrates may lawfully and constitutionally issue "NKW" or "no-knock" warrants where circumstances justify a no-knock entry, and federal law enforcement officers may lawfully apply for such warrants under such circumstances.
by EightSeven June 6, 2010