Related Clues:

• Furtive ''Yo!''
• Note passer's signal
• Readiness condition
• Yellow flag
• Head-turning sound
• Clandestine call
• Near-silent 'Hey!'
• 'Hey … you!'
• Fully conscious
• Hey, the quiet way
• Clear-witted
• Full of NoDoz
• Start of a whispered comment
• Not dozing
• "Hey!" in class