Related Clues:

• Not dozing
• Civilian's 35-Across?
• Not nodding
• 'Look out below!,' e.g.
• Awake and aware
• Having pricked ears
• Keen-eyed
• Like watchmen
• It might be false
• Paying attention
• Like sentries
• Like an excellent guard dog
• Anti-theft device
• On top of things
• Not drowsy