Set the buzzer on or off by physical button or by serial...

buzzer

int btn = 2;
int spkr = 10;
int incomingByte = 0;
int bybtn = 0;
void setup()
{
  Serial.begin(9600);
  Serial.println("Arduino Online");
  Serial.println("..............");
  //setup board
  pinMode(btn, INPUT);
  pinMode(spkr,OUTPUT);
  //initialize the speaker off... may not be needed. 
  digitalWrite(spkr,LOW); 
}
void loop()
{
  if (Serial.available() > 0) {
                // read the incoming byte:
                incomingByte = Serial.read();
                if ( incomingByte == 49 ){
                //received "1"
                digitalWrite(spkr, HIGH);
                Serial.print("Buzzer on ");
                }
                if ( incomingByte == 48){
                //received 0
                digitalWrite(spkr,LOW);
                Serial.print("Buzzer off ");
       
         }

        }
  //stuff to loop
  //read if the button is pressed
  int sensorValue = digitalRead(btn);
  //if pressed make the buzzer buzz
  if( sensorValue == 1){
    digitalWrite(spkr, HIGH);
    bybtn = 1;
    //else buzzzer no buzzzz
  } else {
   if(bybtn){
     digitalWrite(spkr, LOW);
     bybtn = 0; 
   }
  }
}