The Shazalakazoo was a magical musical instrument that Gargamel in the guise of Aurora the good fairy gave to Harmony in "Smurphony In 'C'". It resembled a horn with what appeared to be a squeezable bulb in its middle. It caused whoever listened to its tune played by its player to fall into a deep death-like sleep that they cannot be awakened from.
Harmony was given this musical instrument by Gargamel when the other Smurfs wouldn't let him play along in their symphony due to his off-key music playing. However, it was a way for Gargamel to follow the Smurf into the village when when he played it, causing all his fellow Smurfs and Papa Smurf to go into a deathlike sleep. Later, Harmony used the instrument on Azrael when he went to Gargamel's castle in order to find the cure for it, and also lured Gargamel to a log over a ravine where he nearly fell into it. Unfortunately, Harmony found out from Gargamel's book on magical musical instruments that there's no known cure for those who have listened to the Shazalakazoo's tune, causing him to get so mad that he kicked the musical instrument into the fire, causing sparks to come out as it was burned.
Fortunately, the destruction of the Shazalakazoo was what cured the Smurfs of their deathlike sleep, as Harmony awakened them all to a song from his horn.
The instrument is referred to as a turlisiphone in the original comic book version of "Smurphony In 'C'".