Nothing too fancy about the code, except I wanted the tone of the beeper to change according to how close the detected person was to the camera. This would be useful for discerning the difference between someone posting a letter in the postbox and someone actually walking up the drive. The code uses string analysis functions to, firstly, confirm that the data is coherent by searching for the word 'Box' and then finding the two pairs of coordinates that represent the detection box. If the detected person is close to the camera, the area of the detection box is greater and the resulting alarm tone is of higher frequency:

#include <SPI.h>
#include <LoRa.h>
String myString =" ";
String myStringReversed =" ";

void setup() 
{
  pinMode(4, OUTPUT);
  pinMode(LED_BUILTIN, OUTPUT);
  tone(5,1000,1000);
  digitalWrite(LED_BUILTIN, HIGH);
  digitalWrite(4, HIGH);
  delay(1000);
  digitalWrite(LED_BUILTIN, LOW);
  digitalWrite(4, LOW);
  Serial.begin(9600);
//  while (!Serial);

  Serial.println("LoRa Receiver");

  if (!LoRa.begin(8690E5)) {
    Serial.println("Starting LoRa failed!");
    while (1);
  }
}

void loop() 
{
  //delay (1000);
  // try to parse packet
  int packetSize = LoRa.parsePacket();
  if (packetSize) 
  {
    // received a packet
    Serial.print("Received packet '");
  digitalWrite(LED_BUILTIN, HIGH);
  digitalWrite(4, HIGH);
  delay(100);
  digitalWrite(LED_BUILTIN, LOW);
  digitalWrite(4, LOW);
    // read packet
    myString =" ";
    myStringReversed =" ";
    int i = 0;
    char c;
    while (LoRa.available()) 
    {
      //c[i] = (char)LoRa.read();
      //Serial.print((char)LoRa.read());
      myString = (char)LoRa.read() + myString;
      i++;
      //Reverse the string:
      c = myString.charAt(0);
      myStringReversed = myStringReversed + c;
    }
    processString();
    //Serial.print("My string: ");Serial.print(myString);
    // print RSSI of packet
    //Serial.print("' with RSSI ");
    //Serial.println(LoRa.packetRssi());

  }
}
void processString()
{
    Serial.print("My string reversed:");Serial.print(myStringReversed);
    // print RSSI of packet
    Serial.print("' with RSSI ");
    Serial.println(LoRa.packetRssi());
    int len = myStringReversed.length();
    int j=0;
    char a,b,c,d;
    String coord1 = " ";
    String coord2 = " ";
    String coord3 = " ";
    String coord4 = " ";
    int k =0;
    char x = ',';
    int z=1;
    int y=1;
    int r=1;
    int s=1;
    int v=0;
    while (j < len) 
    {
      a = myStringReversed.charAt(j);
      b = myStringReversed.charAt(j+1);
      c = myStringReversed.charAt(j+2);
      if((a=='B')&&(b=='o')&&(c=='x'))                           // The word 'box' has been identified in the string - k is now greater than 0.
      {
        k = j+5;
        Serial.print("Character B was found at: ");Serial.println(j);
      }
      j++;
    }
    if (k>0)
    {
      v =0;                                                      // int V stops perpetual loops occurring.
      while((z==1)&&(v<200))
      {
        if(myStringReversed.charAt(k)==x)                        // Build up string 'coord' until a comma is reached.
        {
          Serial.print("k");Serial.println(k);
          z=0;
        }
        else
        {
        coord1 = coord1 + myStringReversed.charAt(k);
        k++;
        v++;
        //Serial.print("coord1: ");Serial.println(coord1); 
        }
      } 
      v =0; 
      k++;
      while((y==1)&&(v<200))
      {
        if(myStringReversed.charAt(k)==')')                        // Build up string 'coord' until a comma is reached.
        {
          Serial.print("k");Serial.println(k);
          y=0;
        }
        else
        {
        coord2 = coord2 + myStringReversed.charAt(k);
        k++;
        v++;
        //Serial.print("coord2: ");Serial.println(coord2); 
        }
      }  
      v =0;
      k=k+3;                                                     // Takes account of two brackets and a comma.
      while((r==1)&&(v<200))
      {
        if(myStringReversed.charAt(k)==x)                        // Build up string 'coord' until a comma is reached.
        {
          Serial.print("k");Serial.println(k);
          r=0;
        }
        else
        {
        coord3 = coord3 + myStringReversed.charAt(k);
        k++;
        v++;
        //Serial.print("coord3: ");Serial.println(coord3); 
        }
      }  
      v =0;
      k++;
      while((s==1)&&(v<200))
      {
        if(myStringReversed.charAt(k)==')')                        // Build up string 'coord' until a comma is reached.
        {
          Serial.print("k");Serial.println(k);
          s=0;
        }
        else
        {
        coord4 = coord4 + myStringReversed.charAt(k);
        k++;
        v++;
        //Serial.print("coord4: ");Serial.println(coord4); 
        }
      }  
    }
    Serial.print("coord1: ");Serial.println(coord1);
    Serial.print("coord2: ");Serial.println(coord2);
    Serial.print("coord3: ");Serial.println(coord3);
    Serial.print("coord4: ");Serial.println(coord4);
    int coord10 = coord1.toInt();
    int coord20 = coord2.toInt();
    int coord30 = coord3.toInt();
    int coord40 = coord4.toInt();
    
    int area = (coord40 - coord20) * (coord30 - coord10);
    tone(5,(area/100)+200,100);
    Serial.print("Box area: ");Serial.println(area);
}