Related Clues:

• "Heads up!" e.g
• Keeping one's radar up
• In skill the French sentry should be
• Early warning
• Taking it all in
• Thinking or acting quickly
• Colorful warning, often
• Wide awake to a siren call
• Wide-awake nature
• Danger signal, e.g
• Keenly attentive
• Sharp tip off
• All-points bulletin, e.g
• Like prairie dogs, notably
• Offer a heads-up