let guard down

let (one's) guard down

To become less guarded or vigilant; to stop being cautious about potential trouble or danger. We'll wait long enough for them to let their guard down before we launch our invasion. There will always be people in this business looking to exploit you, so you can never let your guard down.
See also: down, guard, let
Farlex Dictionary of Idioms.

let one's guard down

Fig. to stop guarding oneself against trouble; to relax one's vigilance. He never lets his guard down because he trusts no one.
See also: down, guard, let
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • let (one's) guard down
  • let down (one's) guard
  • leave (one's) guard down
  • lower (one's) guard
  • lower your guard
  • drop (one's) guard
  • be off (one's) guard
  • be on/off your guard
  • on (one's) guard
  • on guard
References in periodicals archive
Real results are close, closer than you judge them to be TO FIND OUT MORE CALL 09050 700 438 CALLS COST 75P/MIN ROI: 1560 911 362 [euro]1.25/MIN LET GUARD DOWN
STARS; SCOTLAND'S TOP ASTROLOGER DAVID WELLS ON THE WEEK AHEAD
He and Williams will kick themselves let guard down at death.
DOUBLE BY DE GUZMAN FOR SWANS AS STOKE FLOUNDER
In the light welterweight category, Brazilian Myke was defensive from the beginning and attacked Kumar who let guard down. Taking advantage of this, Myke scored two points in the first round even as he saved the punches thrown by the Indian.
Indian boxers go down fighting