"The Knock" is a term used in the pirate radio community to refer to an enforcement visit by the FCC. Several pirate radio stations have suffered a bust that was initiated by government agents knocking on the door during a broadcast.
In May 2010, Weather Radio announced the "All weather, all the time" shortwave pirate station would cease operation after getting the knock in April 2010. This is believed to be the first time in more than a decade a US shortwave pirate station received the knock.
In 2007, Todd Daugherty, self-identified operator of Omega One Radio, received a letter from the FCC warning him to discontinue operation. Daugherty's case differed from most U.S. shortwave pirate operations in that he disregarded anonymity and identified himself by name and his amateur radio call sign, N9OGL, which drew the ire of both hams and pirates alike.