This lock is not very difficult to open, so it probably doesn't really count as a puzzle lock, but I like the musical motif. The arm is the locking pin which can be removed when the key is inserted correctly in a hole at the base.
Chinese Brass Lock
Many mechanical puzzles are just for the fun of solving them. This puzzle is designed with a practical purpose-- to thwart thieves.
Click solution to see the rather complicated process to open the lock.