Related Clues:

• 'Heads up!,' e.g.
• Boo-hoo
• See 52-Down
• Scream
• Heads-up
• Argus-eyed
• Watchful
• Whistle, for one
• Warn
• Make a plea for sympathy, maybe
• Caterwaul
• Vigilant
• See 10-Down
• Bawl
• On one's toes