Arduino - Push Button State Problem
you will need to implement a edge sensor. Add a previousTouchsensorState to the globals and replace the if where you check the sensor state with:

if(previousTouchsensorState == LOW &amp;&amp; touchsensorState == HIGH) {                 
     // check if the touch sensor is pressed and wasn't the last time though the loop. 
     // If it is, the touchsensorState is HIGH and previousTouchsensorState is LOW:
     digitalWrite(buzzer, HIGH); // buzzer will emit sound:
     timestamp = millis();       // Timing button press
}
previousTouchsensorState  = touchsensorState;