> when FBI breaks into your house you always know it

That's not true.

  In January 2014, the bureau obtained a court-issued “sneak and peek” warrant,
  allowing agents to secretly search Raphel’s northwest Washington home while
  she was away.

  The FBI sent a special Evidence Response Team trained in surreptitious
  searches. Raphel’s home had an alarm system, which the FBI team bypassed.

http://www.wsj.com/articles/the-last-diplomat-1480695454