Wiktionary
vb. 1 (context idiomatic English) To maintain vigilance for someone or something. 2 (context idiomatic English) To maintain vigilance for a possibly dangerous situation.
Usage examples of "keep an eye open".
His superiors had passed on a warning from the Keeper that there had been a major battle on the other side of the mountains, Outside, and that recorders in the area must keep an eye open for refugees sneaking into Thume.
She made a mental note to keep an eye open for a nice young man for Jay, and rejoined the others.
I could have my assistant keep an eye open for you, but he hasn't come in for a week.
Well keep an eye open for scarecrow clothes on the way, he added, lowering his voice.
Toffner obtained a hotel room and then visited the current trade mart, hoping to keep an eye open for items suitable for future gladiator fights.
I had told my friends everything I'd learned, and they were primed to keep an eye open for Liz Connor, for Mr.