Related Clues:

• Signed up for
• Put down
• Aware, with 'in'
• Attuned
• Nervous, with 'up'
• Recorded
• Registered
• Tensed, with 'up'
• Atwitter, with 'up'
• Excited, with 'up'
• Worked (up)
• Penetrated
• Input
• Came in
• Walked in