user47469: I am trying to develop a burglar alert system. I am using PIR sensor, Arduino Mega and SIM800L. I have connected PIR sensor to interrupt pin. Whenever motion is dected, a function corresponding to the interrupt will be called. In that function I am sending a SMS to notify with an alert message. If motion is detected 2 times, I will call the emergency contact number.
This is the code I have written.
#include <SoftwareSerial.h>
#define PIR1 2
#define SIREN 13
#define statusLED 12

SoftwareSerial SMS(11, 10);// rx(11-arduino) connect to tx(gsm module)
                         // tx(10-arduino) connect to rx(gsm module)

String CONTACT1 = "xxxxxxxxxx";  //mobile number


boolean status;
byte motionCtr = 0;
unsigned long latestMovementTime = 0;

void setup() {
  pinMode(PIR1,INPUT);
  pinMode(SIREN,OUTPUT);
  pinMode(statusLED,OUTPUT);

  Serial.begin(9600);
  SMS.begin(9600); 
  SMS.println("AT+CNMI=2,2,0,0,0");

  delay(5000);
  activateSystem(0);
}


void loop() {
  unsigned long currentTime = millis();
  //If motion is not dected for 5 minutes, turn off the siren.
  if(currentTime - latestMovementTime > 300000 && motionCtr>=1){
    stopSiren(0);  
  }
  delay(500);
}

void activateSystem(byte manual){
  delay(60000); //warm up time for PIR sensor
  attachInterrupt(0,motionDetected,RISING);

  status = true; 
  digitalWrite(statusLED,HIGH);

  if(manual){
    Serial.println("System ACTIVATED by SMS.");
    notifyBySMS("System ACTIVATED SMS.");
  }else{
    Serial.println("System ACTIVATED.");
    notifyBySMS("System ACTIVATED.");
  }
}

void deactivateSystem(byte manual){
  detachInterrupt(0);

  status = false;
  digitalWrite(statusLED,LOW);

  if(manual){
    Serial.println("System DEACTIVATED by SMS.");
    notifyBySMS("System DEACTIVATED SMS.");
  }else{
    Serial.println("System DEACTIVATED.");
    notifyBySMS("System DEACTIVATED.");
  }
}

void motionDetected(){
  startSiren("Motion at bedroom door.");
}


void startSiren(String msg){
  //Record the time of latest motion dected.
  latestMovementTime = millis();

  motionCtr++;
  Serial.print("Ctr="+motionCtr);
  Serial.println(msg);
  notifyBySMS(msg);

  //Start the siren only if motion is detected 2 times
  if(motionCtr==2){
    digitalWrite(SIREN,HIGH);  
    Serial.println("Siren STARTED.");
    notifyBySMS("Siren STARTED.");
    call(CONTACT1);
//    call(CONTACT2);
//    call(CONTACT3);
  }
}


void stopSiren(byte manual){
  motionCtr = 0;
  Serial.println("Ctr="+motionCtr);
  digitalWrite(SIREN,LOW);
  if(manual){
    Serial.println("Siren STOPPED manually.");
    notifyBySMS("Siren STOPPED manually.");
  }else{
    Serial.println("Siren STOPPED");
    notifyBySMS("Siren STOPPED.");
  }
}


void sendSMS(String mobileNumber, String msg){
  Serial.println("Sending SMS to "+mobileNumber);
  //AT command for text mode of gsm module 
  SMS.println("AT+CMGF=1"); 
  delay(100);  
  SMS.println("AT+CMGS=\""+mobileNumber+"\"\r"); 
  delay(100);
  // the text you want to send
  SMS.println(msg);
  delay(100);
  // ASCII code of CTRL+Z
  SMS.println((char)26);
  delay(5000);
  Serial.println("SMS sent to "+mobileNumber);
}

void call(String mobileNumber){
  Serial.println("Calling..."+mobileNumber);
  SMS.println("AT+CMGF=0"); //AT command for PDU mode of gsm module 
  SMS.println("ATD"+mobileNumber+";");
  delay(45000);
  SMS.println("ATH");
}


void notifyBySMS(String msg){
  sendSMS(CONTACT1,msg);
  delay(1000);
//  sendSMS(CONTACT2,msg);
//  delay(1000);
//  sendSMS(CONTACT3,msg);
//  delay(1000);
}

I am receiving the SMS from setup(). But I am not receiving the SMS that I have sent from interrupt routine. Also I am receiving the call only sometime, it is random. I guess this is because I am using delay() in interrupt routine.
How can I implement such logic without delay(). 

user337: As mentioned in the comments Serial won't work in an ISR. Generally, you should do as little as possible in an ISR. Often an ISR will just set a flag to be handled in loop()
You will then need to refactor loop() to handle the flag set in the ISR. A common method is to use a finite state machine.

47469: <p>I am trying to develop a burglar alert system. I am using PIR sensor, Arduino Mega and SIM800L. I have connected PIR sensor to interrupt pin. Whenever motion is dected, a function corresponding to the interrupt will be called. In that function I am sending a SMS to notify with an alert message. If motion is detected 2 times, I will call the emergency contact number.</p>

<p>This is the code I have written.</p>

<pre><code>#include &lt;SoftwareSerial.h&gt;
#define PIR1 2
#define SIREN 13
#define statusLED 12

SoftwareSerial SMS(11, 10);// rx(11-arduino) connect to tx(gsm module)
                         // tx(10-arduino) connect to rx(gsm module)

String CONTACT1 = "xxxxxxxxxx";  //mobile number


boolean status;
byte motionCtr = 0;
unsigned long latestMovementTime = 0;

void setup() {
  pinMode(PIR1,INPUT);
  pinMode(SIREN,OUTPUT);
  pinMode(statusLED,OUTPUT);

  Serial.begin(9600);
  SMS.begin(9600); 
  SMS.println("AT+CNMI=2,2,0,0,0");

  delay(5000);
  activateSystem(0);
}


void loop() {
  unsigned long currentTime = millis();
  //If motion is not dected for 5 minutes, turn off the siren.
  if(currentTime - latestMovementTime &gt; 300000 &amp;&amp; motionCtr&gt;=1){
    stopSiren(0);  
  }
  delay(500);
}

void activateSystem(byte manual){
  delay(60000); //warm up time for PIR sensor
  attachInterrupt(0,motionDetected,RISING);

  status = true; 
  digitalWrite(statusLED,HIGH);

  if(manual){
    Serial.println("System ACTIVATED by SMS.");
    notifyBySMS("System ACTIVATED SMS.");
  }else{
    Serial.println("System ACTIVATED.");
    notifyBySMS("System ACTIVATED.");
  }
}

void deactivateSystem(byte manual){
  detachInterrupt(0);

  status = false;
  digitalWrite(statusLED,LOW);

  if(manual){
    Serial.println("System DEACTIVATED by SMS.");
    notifyBySMS("System DEACTIVATED SMS.");
  }else{
    Serial.println("System DEACTIVATED.");
    notifyBySMS("System DEACTIVATED.");
  }
}

void motionDetected(){
  startSiren("Motion at bedroom door.");
}


void startSiren(String msg){
  //Record the time of latest motion dected.
  latestMovementTime = millis();

  motionCtr++;
  Serial.print("Ctr="+motionCtr);
  Serial.println(msg);
  notifyBySMS(msg);

  //Start the siren only if motion is detected 2 times
  if(motionCtr==2){
    digitalWrite(SIREN,HIGH);  
    Serial.println("Siren STARTED.");
    notifyBySMS("Siren STARTED.");
    call(CONTACT1);
//    call(CONTACT2);
//    call(CONTACT3);
  }
}


void stopSiren(byte manual){
  motionCtr = 0;
  Serial.println("Ctr="+motionCtr);
  digitalWrite(SIREN,LOW);
  if(manual){
    Serial.println("Siren STOPPED manually.");
    notifyBySMS("Siren STOPPED manually.");
  }else{
    Serial.println("Siren STOPPED");
    notifyBySMS("Siren STOPPED.");
  }
}


void sendSMS(String mobileNumber, String msg){
  Serial.println("Sending SMS to "+mobileNumber);
  //AT command for text mode of gsm module 
  SMS.println("AT+CMGF=1"); 
  delay(100);  
  SMS.println("AT+CMGS=\""+mobileNumber+"\"\r"); 
  delay(100);
  // the text you want to send
  SMS.println(msg);
  delay(100);
  // ASCII code of CTRL+Z
  SMS.println((char)26);
  delay(5000);
  Serial.println("SMS sent to "+mobileNumber);
}

void call(String mobileNumber){
  Serial.println("Calling..."+mobileNumber);
  SMS.println("AT+CMGF=0"); //AT command for PDU mode of gsm module 
  SMS.println("ATD"+mobileNumber+";");
  delay(45000);
  SMS.println("ATH");
}


void notifyBySMS(String msg){
  sendSMS(CONTACT1,msg);
  delay(1000);
//  sendSMS(CONTACT2,msg);
//  delay(1000);
//  sendSMS(CONTACT3,msg);
//  delay(1000);
}
</code></pre>

<p>I am receiving the SMS from <code>setup()</code>. But I am not receiving the SMS that I have sent from interrupt routine. Also I am receiving the call only sometime, it is random. I guess this is because I am using <code>delay()</code> in interrupt routine.</p>

<p>How can I implement such logic without <code>delay()</code>. </p>
 337: <p>As mentioned in the comments Serial won't work in an ISR. Generally, you should do as little as possible in an ISR. Often an ISR will just set a flag to be handled in <code>loop()</code></p>

<p>You will then need to refactor <code>loop()</code> to handle the flag set in the ISR. A common method is to use a <a href="https://en.wikipedia.org/wiki/Finite-state_machine" rel="nofollow noreferrer">finite state machine</a>.</p>
