Related Clues:

• Cry 'Heads up!' to
• Cautioned
• Give a heads-up to
• Raise red flags
• Notify of potential danger
• Give a heads-up
• Issue a caveat
• On notice
• Give an alert
• Sound the alarm
• Notify in advance
• Honk at, perhaps
• Notified of danger
• Give an alert (to)
• Shoot off a flare, e.g.