Alarm system

1int trigPin = 9;//first we should the pins
2int echoPin = 10;
3int  buzzer  = 7;
4void setup() {
5  Serial.begin (9600);//to print on serial moniter  we should start the serial baud
6  pinMode(trigPin, OUTPUT);//we should declare  trigpin as output and echo pin as input
7  pinMode(echoPin, INPUT);
8  pinMode(buzzer,  OUTPUT);
9}
10
11void loop() {
12  //block of code used to find the distance  of an object in cm 
13  long duration, distance;
14  digitalWrite(trigPin, LOW);
15  delayMicroseconds(2);
16  digitalWrite(trigPin, HIGH);
17  delayMicroseconds(10);
18  digitalWrite(trigPin, LOW);
19  duration = pulseIn(echoPin, HIGH);
20  distance  = (duration / 2) / 29.1;
21  
22  if (distance <= 10)// if the distance is less  than 10 or = 10 
23                    //than the buzzer will make sound
24  {
25    digitalWrite(buzzer,HIGH);
26    Serial.print(distance);//to print the distance  in serial moniter
27    Serial.println("");
28  }
29  else {
30   digitalWrite(buzzer,LOW);//else  it will turn off
31   Serial.print(distance);//to print the distance in serial  moniter
32   Serial.println("");
33  }
34  delay(10);
35}