'Lookout' in the Bible

And evil shall come upon you, you will not know; it will be on the lookout for her. And disaster shall fall upon you; you will not be able to {avert} it. And ruin shall come on you suddenly; you do not know.

Now I exhort you, brothers, to look out for those who cause dissensions and temptations contrary to the teaching which you learned, and stay away from them.