On this instructables, I will share how to build security system with atmega8 arduino,

Step 1: Building an Arduino Standalone With Atmega8

Check here : http://arduino.cc/en/Main/Standalone

or you can use any type of arduino

Step 2: Wire the LDR, BUZZER and Led

Connect LDR to 5v and A0,

from A0 use resistor any value to GND

LED to pin13 and GND

buzzer to pin7

Step 3: Soldering Potensiometers

Solder pin1 to GND arduino

pin2 to A1 arduino

pin3 to 5v arduino

Step 4: Wire Laser Diode

Wire blue cable to GND and Red to 5v

or use 3-5v battery

Step 5: Soldering USB Jack

use usb jack for the power of my project, so the project can work from a laptop or pc

wire the + pin to 5+ arduino and GND to GND arduino,

Step 6: The Code

int sensorPin = A0;  
int potensioPin = A1;
int ledPin = 13;     
int sensorValue = 0; 
int potensioValue = 0;
int laserPin = 12;

void setup() {
  //Serial.begin(9600);
  pinMode(ledPin, OUTPUT);  
  pinMode(2, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(6, OUTPUT);
  pinMode(7, OUTPUT);
  pinMode(8, OUTPUT);
  pinMode(9, OUTPUT);
  pinMode(10, OUTPUT);
  pinMode(11, OUTPUT);  
  pinMode(laserPin, OUTPUT);
}

void loop() {
  digitalWrite(laserPin, HIGH);
  sensorValue = analogRead(sensorPin);    
  potensioValue = analogRead(potensioPin);   
  sensorValue = map(sensorValue, 0, 1023, 0, 100);
  potensioValue = map(potensioValue, 0, 1023, 0, 100);
  //Serial.println(potensioValue);  if(sensorValue < 99){
    digitalWrite(5, HIGH);
    digitalWrite(6, HIGH);
    digitalWrite(7, HIGH);
    digitalWrite(8, HIGH);
    digitalWrite(9, HIGH);
    digitalWrite(10, HIGH);
    digitalWrite(11, HIGH);
        for(int i=0; i <= potensioValue; i++){
      digitalWrite(ledPin, HIGH);
      delay(100);
      digitalWrite(ledPin, LOW);
      delay(100);
      buzz(7, 2500, 200);
      buzz(9, 2500, 200);  
        if(i == potensioValue)
        {
          buzz(2, 2500, 100 * potensioValue);
          buzz(9, 2500, 100 * potensioValue);  
          digitalWrite(5, LOW);
          digitalWrite(6, LOW);
          digitalWrite(7, LOW);
          digitalWrite(8, LOW);
          digitalWrite(9, LOW);
          digitalWrite(10, LOW);
          digitalWrite(11, LOW);
        }
    }
   
  }      
  }

void buzz(int targetPin, long frequency, long length) {
  long delayValue = 1000000/frequency/2; 
  long numCycles = frequency * length/ 1000; 
 for (long i=0; i < numCycles; i++){ 
    digitalWrite(targetPin,HIGH); 
    delayMicroseconds(delayValue); 
    digitalWrite(targetPin,LOW); 
    delayMicroseconds(delayValue); 
  }
}

thanks to read this instructables and i hope this useful..