// Techatronic.com
 // Download Library of SoftwareSerial link given
 // https://github.com/PaulStoffregen/SoftwareSerial

 // GSM based home security system 
 
  #include <SoftwareSerial.h>
  SoftwareSerial SIM900A(10,11);  // SoftSerial( RX , TX );
 // 10 pin connect to TX of GSM SIM 900 Module
 // 11 pin connect to RX of GSM SIM 900 Module

int val = 0 ;
void setup()
{
    
    Serial.begin(9600);   // sensor buart rate
    SIM900A.begin(9600);  // GSM buart rate
    pinMode(4,HIGH);      // LED connect D4
   
    
}
void loop() 
{
  val = digitalRead(7);  //  IR sensor output pin connected D7
  Serial.println(val);   // see the value in serial mpnitor in Arduino IDE
  delay(1000);

  if (Serial.available()>0)
   switch(Serial.read())

    if (SIM900A.available()>0)
   Serial.write(SIM900A.read());
  
  if(val == 0 )  // Check your sensor Value 1 or 0
  // in my case IR sensor detect then value is 0 otherwise 1 you can change value
  {
     Serial.println ("Obstacle Detecting");
     digitalWrite(4,HIGH);   // LED ON
    Serial.println ("Sending Message");
  SIM900A.println("AT+CMGF=1");    //Sets the GSM Module in Text Mode
  delay(1000);
  Serial.println ("Set SMS Number");
   SIM900A.println("AT+CMGS=\"xxxxxxxxxx\"\r"); //Mobile phone number to send message, replace x by your number
  delay(1000);
  Serial.println ("Set SMS Content");
  SIM900A.println("Some one IS comming, be safe");// Messsage content
  delay(100);
  Serial.println ("Finish");
  SIM900A.println((char)26);// ASCII code of CTRL+Z
  
  delay(1000);
  Serial.println ("Message has been sent ");
  digitalWrite(4,LOW);   // LED OFF
   
  }
  }