Example : Bombers were put on alert during the crisis.

Synonyms : qui vive

Synonyms : alerting

Synonyms : alarm, alarum, warning signal

Example : Caught by a couple of alert cops.
Alert enough to spot the opportunity when it came.
Constantly alert and vigilant, like a sentinel on duty.

Synonyms : watchful

Example : A brisk walk in the park.
A lively gait.
A merry chase.
Traveling at a rattling rate.
A snappy pace.
A spanking breeze.

Synonyms : brisk, lively, merry, rattling, snappy, spanking, zippy

Example : An alert mind.
Alert to the problems.
Alive to what is going on.
Awake to the dangers of her situation.
Was now awake to the reality of his predicament.

Synonyms : alive, awake

Example : The empty house alarmed him.
We alerted the new neighbors to the high rate of burglaries.

Synonyms : alarm