keep an eye out for

keep an eye out for somebody/something

to watch carefully for someone or something to appear Keep an eye out for signposts for Yosemite.
See also: eye, keep, out

keep an eye out for

Also, keep a sharp lookout for. Be watchful for something or someone, as in Keep an eye out for the potholes in the road, or They told him to keep a sharp lookout for the police. The first expression, sometimes amplified to keep a sharp eye out for, dates from the late 1800s, the variant from the mid-1700s. Also see have one's eye on, def. 1; keep a weather eye; keep one's eyes open; look out.
See also: eye, keep, out
References in classic literature ?
It's a sure good idea to keep an eye out for town sites all the way up.
Allowed to roam the building alone, call on friends on different floors, ride the lifts and play in the gardens without an adult in tow - because all neighbours will keep an eye out for them - they quickly become self-sufficient.