Using music and musical instruments as security measures. Pianos or similar instruments are common, as you are blatantly dealing with keys. Can often be the way to conceal your secret lair by being Hidden in Plain Sight. The tune itself may be significant/ironic, or the Theme tune or Leitmotif of a character.
Subtrope of Solve the Soup Cans. Compare with Musical Trigger. Can be related to Only [...] [tvtropes.org]