смотреть в оба {v. phr.}
smotr'et' v oba
{literally} to look through both.
To look attentively; to be closely observant; to be on the alert; to be particularly watchful.
Comp.:
to keep one's eyes peeled/skinned.
See also:
(смотреть) во все глаза
все глаза проглядеть