PIR sesor with power saving

pir.ino

#include <avr/sleep.h>

const int32_t led_pin = 13;
const int32_t pir_input_pin = 2;

int32_t pir_state = LOW;
volatile int32_t pinval = 0;

void setup() 
{
  pinMode(led_pin, OUTPUT);      
  pinMode(pir_input_pin, INPUT);     
  
  
  Serial.begin(115200);
  Serial.println("Armed");
  Serial.flush();
  attachInterrupt(digitalPinToInterrupt(pir_input_pin), pir_irq_handler, CHANGE);
  
}

void loop() 
{
  // put your main code here, to run repeatedly:
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);  
  sleep_enable();
  sleep_mode();
  sleep_disable();
}

void pir_irq_handler()
{
  sleep_disable();

  pinval = digitalRead(pir_input_pin);
  
  if(pinval == HIGH)
  {
    digitalWrite(led_pin, HIGH);
    if(pir_state == LOW)
    {
      Serial.println("Target movement Detected");
      Serial.flush();
      pir_state = HIGH;  
    }
  
  }

  if(pinval == LOW)
  {
    digitalWrite(led_pin, LOW);
    if(pir_state == HIGH)
    {
      Serial.println("Target Lost");
      Serial.flush();
      pir_state = LOW;  
    }
  
  }
}