NRF24l01 sender....

sensor.ino

#include <RF24.h>
#include <SPI.h>

// PIR variables
byte pirPin = 2;
int pirCalibrationTime = 30;

// Radio with CE & CSN connected to pins 7 & 8
RF24 radio(7, 8);

// Constants that identify this node and the node to send data to
const uint16_t this_node = 1;
const uint16_t parent_node = 0;

// Time between packets (in ms)
const unsigned long interval = 10000;  // every TEN sec

// Structure of our message
struct message_1 {
  bool motion;
};
message_1 message;

void setup(void)
{
  // Set up the Serial Monitor
  Serial.begin(9600);

  // Initialize all radio related modules
  SPI.begin();
  radio.begin();
  delay(5);

  // Calibrate PIR
  pinMode(pirPin, INPUT);
  digitalWrite(pirPin, LOW);
  Serial.print("Calibrating PIR ");
  for(int i = 0; i < pirCalibrationTime; i++)
  {
    Serial.print(".");
    delay(1000);
  }
  Serial.println(" done");
  Serial.println("PIR ACTIVE");
  delay(50);
}

void loop() {

  // Read motion: HIGH means motion is detected
  bool m = (digitalRead(pirPin) == HIGH);
  
  // Construct the message we'll send
  message = (message_1){ m };

  // Writing the message to the network means sending it
  if (radio.write(&message, sizeof(message))) {
    Serial.print("Message sent\n"); 
  } else {
    Serial.print("Could not send message\n"); 
  }

  // Wait a bit before we start over again
  delay(interval);
}