Alert

Part of speech: noun (n.)

An alarm from a real or threatened attack; a sudden attack; also, a bugle sound to give warning. "We have had an alert." Farrow. On the alert, on the lookout or watch against attack or danger; ready to act.

Part of speech: adjective (a.)

1. Watchful; vigilant; active in vigilance.

2. Brisk; nimble; moving with celerity. An alert young fellow. Addison.

Synonyms: Active; agile; lively; quick; prompt.