Related Clues:

• Vigilantly attentive
• Not out of it
• Important
• *Siren ... danger ... perked up
• Extraordinary
• Warning
• A wink or a nod, perhaps
• Perceptive
• Sound the tocsin
• Notable
• On your toes
• With eyes wide open
• Mentally responsive
• It may be red
• Nod, at auctions