Related Clues:

• On top of things
• Not drowsy
• Word with red or on
• Observant
• Put on guard
• Red state?
• Like a worthy watchdog
• Having heightened senses
• APB, for one
• A serious one may be red
• Storm warning
• Emulate Paul Revere
• "Fore!" for one
• Give a heads-up to
• Readiness condition