How to use "alert" in a sentence

She would need to be fresh and alert in the morning.

His eyes were green, clear, alert, and - if one took the time to study them - menacing

When they had landed, they'd been alert for unusual activity on the runway and in the private-craft docking yard - suspicious vehicles, an unusual number of ground crewmen - but they had seen nothing out of the ordinary

Apparently afraid that she would voice her thoughts and alert Dombey to the incredible truth of the situation, Elliot consulted his wristwatch and said, "We ought to get out of here."