Possible Clues:

• Makes use of
• Soldier's good night tune
• Last melody?
• Turn them on for knocks for the blows at last
• Reveille counterpart
• "ights out"bugle tune
• Turn them off and turn the lights off in the US army
• Eavesdroppers' equipment
• It's bugled on a base
• Shortly, what central heating will reveal knocks?