Related Clues:

• Raise red flags
• Not dozing
• Fully attentive
• Notify of potential danger
• Like good watchmen
• Fully awake
• Bright-eyed
• Issue a caveat
• Give an alert
• Type of post-caffeine state
• Percipient
• ''Heads up!'' e.g.
• Sound the alarm
• Notify in advance
• Far from drowsy