be wary

See: beware
References in classic literature ?
They are other clouds and blacker threat you, dame; You must be wary, and pull in your sails, And yield unto the weather of the tempest.
On the contrary, the women have ten thousand times the more reason to be wary and backward, by how much the hazard of being betrayed is the greater; and would the ladies consider this, and act the wary part, they would discover every cheat that offered; for, in short, the lives of very few men nowadays will bear a character; and if the ladies do but make a little inquiry, they will soon be able to distinguish the men and deliver themselves.
For a long time their blows met like the steady crackling of some huge forest fire, and Eric strove to be wary, for he now knew that the other had no mean wits or mettle.
We rose, and crept out of the hut to see what it might be that stirred, for the night drew on, and it was needful to be wary, since a dog might bark at the stirring of a leaf, or perhaps it might be the distant footfall of an impi that it heard.