Code to be used with a HC SC04 Ultrasound Detector Module (USDM)

With this code it will take a button to be pressed to turn the sensor on; once this has happened the distance will be sent to the Serial. 
When an object is detected then a buzzer will buzz with increased length and volume as the object gets closer.
On another button press the system will stop recording the USDM's readings, meaning the buzzer does not make a noise.