Door Alarm With Ultrasonic Sensor

1const int TrigPin = 2;
2const int EchoPin = 3;
3const int Data = 8;
4float  cm;
5void setup()
6{
7  Serial.begin(9600);
8  pinMode(TrigPin, OUTPUT);
9  pinMode(EchoPin, INPUT);
10  pinMode(Data,OUTPUT);
11}
12void loop()
13{
14  digitalWrite(TrigPin, LOW);       
15  delayMicroseconds(2);
16  digitalWrite(TrigPin,  HIGH);
17  delayMicroseconds(10);
18  digitalWrite(TrigPin, LOW);
19  cm = pulseIn(EchoPin,  HIGH) / 58.0; //The echo time is converted into cm
20  cm = (int(cm * 100.0)) /  100.0;     //Keep two decimal places
21  Serial.println();
22  if(cm<15){ //if  you are puting the sensor behind the door use ">" sysmbole insted of ">" p.s.  make sure tat the door nob is less than 15 cm away
23      digitalWrite(Data,HIGH);
24      delay(200);
25      Serial.print("Door closed");
26    }
27    else
28    {
29      digitalWrite(Data,LOW);
30      delay(200);  
31      Serial.print("Door  open");
32    }
33  delay(200);
34}
35