The sensor connects in series with a resitor. Middle point to an analog input.
Resistor value approx same as sensors resistance
The sentence: v=analogRead(inputpin); will return a value near 500 (depending on serial R)
Your program loop check for change in that value..
something like:
if (v<val1 || v>val2) action(); // where 'action' is the function that sounds the buzzer.
You make sound by switching power on/off to the element
digitalWrite(pin,HIGH); // then LOW - repeating in a loop. a short delay can change frequency