#define trigPin1 9                                   
#define echoPin1 8                                   
#define buzzer1  2                            
#define trigPin2 10
#define echoPin2 11
#define buzzer2  4
long duration, distance, UltraSensor1, UltraSensor2; 
char data;
String SerialData="";
void setup()
{
Serial.begin (9600);                         

pinMode(trigPin1, OUTPUT);                        
pinMode(echoPin1, INPUT);                         
pinMode(buzzer1, OUTPUT);                  

pinMode(trigPin2, OUTPUT);
pinMode(echoPin2, INPUT);
pinMode(buzzer2, OUTPUT);


digitalWrite(buzzer1,LOW);
digitalWrite(buzzer2,LOW);
}
void loop() 
{
SonarSensor(trigPin1, echoPin1);              
UltraSensor1 = distance;                      
SonarSensor(trigPin2,echoPin2);               
UltraSensor2 = distance;                      

while(Serial.available())
{
  delay(10);
  data=Serial.read();
  SerialData+=data;
}

if(SerialData=="display distance")
{

Serial.print("distance measured by the first sensor: ");
Serial.print(UltraSensor1);
Serial.println(" cm");

Serial.print("distance measured by the second sensor: ");
Serial.print(UltraSensor2);
Serial.println(" cm");
Serial.println("---------------------------------------------------------------------------------------------------------");
}

SerialData="";
if(UltraSensor1 <=10)
{
  digitalWrite(buzzer1,HIGH);
}
else                
{
  digitalWrite(buzzer1,LOW);
}

if(UltraSensor2 <=10)
{
  digitalWrite(buzzer2,HIGH);
}
else
{
  digitalWrite(buzzer2,LOW);
}
}

void SonarSensor(int trigPinSensor,int echoPinSensor) 
{
digitalWrite(trigPinSensor, LOW); 
delayMicroseconds(2);
digitalWrite(trigPinSensor, HIGH);
delayMicroseconds(10); 
digitalWrite(trigPinSensor, LOW);
duration = pulseIn(echoPinSensor, HIGH);
distance= (duration/2) / 29.1;
 }