Pregunta activar/desactivar sensor PIR

Buenas !! a toda la comunidad mi consulta es la siguiente :
tengo el programa y el sensor pir funcionando pero yo quiero que con una letra por ejemplo la “A” se active el sensor y con la “B” se desactive este es el el codigo que estoy usando de antemano gracias !!

int ledPin = 13; // choose the pin for the LED
int inputPin = 2; // choose the input pin (for PIR sensor)
int pirState = LOW; // we start, assuming no motion detected
int val = 0; // variable for reading the pin status
int pinSpeaker = 10; //Set up a speaker on a PWM pin (digital 9, 10, or 11)

void setup() {
pinMode(ledPin, OUTPUT); // declare LED as output
pinMode(inputPin, INPUT); // declare sensor as input
pinMode(pinSpeaker, OUTPUT);
Serial.begin(9600);
}

void loop(){
val = digitalRead(inputPin); // read input value
if (val == HIGH) { // check if the input is HIGH
digitalWrite(ledPin, HIGH); // turn LED ON
playTone(300, 160);
delay(150);

if (pirState == LOW) {
// we have just turned on
Serial.println(“Motion detected!”);
// We only want to print on the output change, not state
pirState = HIGH;
}
} else {
digitalWrite(ledPin, LOW); // turn LED OFF
playTone(0, 0);
delay(300);
if (pirState == HIGH){
// we have just turned of
Serial.println(“Motion ended!”);
// We only want to print on the output change, not state
pirState = LOW;
}
}
}
// duration in mSecs, frequency in hertz
void playTone(long duration, int freq) {
duration *= 1000;
int period = (1.0 / freq) * 1000000;
long elapsed_time = 0;
while (elapsed_time < duration) {
digitalWrite(pinSpeaker,HIGH);
delayMicroseconds(period / 2);
digitalWrite(pinSpeaker, LOW);
delayMicroseconds(period / 2);
elapsed_time += (period);
}
}

Saludos
Me imagino que a estas alturas ya solucionaste pero sino aquí te dejo esto:

int ledPin = 13;                // choose the pin for the LED
int inputPin = 2;               // choose the input pin (for PIR sensor)
int pirState = LOW;             // we start, assuming no motion detected
int val = 0;                    // variable for reading the pin status
int pinSpeaker = 10;           //Set up a speaker on a PWM pin (digital 9, 10, or 11)
boolean estado = false;
void setup() {
  pinMode(ledPin, OUTPUT);      // declare LED as output
  pinMode(inputPin, INPUT);     // declare sensor as input
  pinMode(pinSpeaker, OUTPUT);
  Serial.begin(9600);
}

void loop(){
  if (Serial.available()){
    int comando = Serial.read();
     if (comando == 'A'){estado= true;}
     if (comando == 'B'){estado= false;}
    }
 if (estado == true){
   activo();
  }   
}

// duration in mSecs, frequency in hertz


void activo(){
    val = digitalRead(inputPin);  // read input value
  if (val == HIGH) {            // check if the input is HIGH
    digitalWrite(ledPin, HIGH);  // turn LED ON
    playTone(300, 160);
    delay(150);

    
    if (pirState == LOW) {
      // we have just turned on
      Serial.println("Motion detected!");
      // We only want to print on the output change, not state
      pirState = HIGH;
    }
  } else {
      digitalWrite(ledPin, LOW); // turn LED OFF
      playTone(0, 0);
      delay(300);    
      if (pirState == HIGH){
      // we have just turned of
      Serial.println("Motion ended!");
      // We only want to print on the output change, not state
      pirState = LOW;
    }
  }

}


void playTone(long duration, int freq) {
    duration *= 1000;
    int period = (1.0 / freq) * 1000000;
    long elapsed_time = 0;
    while (elapsed_time < duration) {
        digitalWrite(pinSpeaker,HIGH);
        delayMicroseconds(period / 2);
        digitalWrite(pinSpeaker, LOW);
        delayMicroseconds(period / 2);
        elapsed_time += (period);
    }
}