be on the look out

be on the lookout

To be watching for something or someone. Be on the lookout for my email! It will have all the instructions you need for the project. A: "What are you guys doing?" B: "We're on the lookout for Mom's car, so we can tell Dad to stop working on her surprise gift when she gets here."
See also: lookout, on
Farlex Dictionary of Idioms.

be on the look out

and BOLO
phr. & comp. abb. establish and maintain surveillance [for someone]. (A police notation.) BOLO for a 65-year-old woman with tattoos on her upper arms. We’ll be on the look out for your stolen car.
See also: look, on, out
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • be on the lookout
  • on the lookout
  • bolo
  • mount guard
  • mount/stand/keep guard
  • keep guard
  • mount
  • stand guard
  • have a thing for (something)
  • access