Step 11: What's the polarity?
With more luck, the tone will change when you get the sensor near a magnet.
Hang a magnet by a string or float it. The end pointing North is North.
On mine, the pitch goes up with the south pole of a magnet near the bottom of the sensor.
And down with a north pole near the bottom.
And up with the north pole near the top.
And down with the south pole near the top.