arduinokov:
int thisPitch=map(sensorReading, 400, 1000, 120, 1500);
tone(9, thisPitch, 10);
That would seem to define a frequency in the range 120Hz - 1500Hz and play it for 10 milliseconds. Those frequencies seem a little on the low side and you might want to compare them with the range supported by your speaker (small speakers don't usually support low frequencies). The duration of 10ms is obviously far too short to be heard. Perhaps you intended 10000ms (ten seconds)?