Related Clues:

• Percipient
• ''Heads up!'' e.g.
• Sound the alarm
• Notify in advance
• Far from drowsy
• Honk at, perhaps
• Not asleep on the job
• Notified of danger
• Storm posting, e.g.
• Warning notice
• Give an alert (to)
• Like a sentry
• Bushy-tailed?
• Red __
• Shoot off a flare, e.g.