This is an Instructable that tells you how to make a laser tripwire or laser maze, just like in the movies!

All you need:

* Arduino
* Buzzer/alarm/Led
* Led (optional)
* 1 resistor (any value)
* 1 LDR
* Laser pen
* A box to house the entire set up.
* Some tape

See it in Action:

http://www.youtube.com/watch?v=74KYPlzEGqc

http://www.youtube.com/watch?v=56aGdz3GAW0

Step 1: Step 1

* Attach the resistor to A0 and Gnd pins.
* Attach LDR to A0 and 5 V pins.
* Place an LED with longer side in pin 7 and shorter side in pin 6.
* Also place the buzzer with longer side in pin 11 and shorter side in Gnd pin.

Step 2: Step 3:

*Place the contraption in the box (to make it look neat as well as keep it hidden )

*Upload the following program on arduino:

///PROGRAM STARTS FROM BELOW

int sensorPin = A0;
int sensorValue = 0;
int buzzPin=11;

void setup() {
    pinMode(buzzPin, OUTPUT);
pinMode(sensorPin, INPUT);
pinMode(7, OUTPUT);
pinMode(6, OUTPUT);
digitalWrite(7,HIGH);
digitalWrite(6,LOW);
delay(5000);
digitalWrite(7,LOW);
}

void loop() {

sensorValue = analogRead(sensorPin);
if(sensorValue<=500)
{digitalWrite(buzzPin, HIGH);
delay(3000);}
else
{digitalWrite(buzzPin, LOW);}
sensorValue=1000;
}

*Now tape the button on the laser to keep it on.
*Finally place the laser away from the box and make sure that its light is concentrated on the LDR.

Step 3: FINALLY!!

POWER UP AND ENJOY!!

You can add mirrors to form a maze by reflecting the laser light.
You can also place this in front of a door or window and it will act like an alarm if the door or window opens.
It can also be placed across the ends of a room and be used as a motion sensor

To actually see the laser light ( like in the photo) all you have to do is shroud the room in smoke. The laser light can be seen in smoke.
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Feel free to ask any doubts and please give me feedback and other suggestions.

Thank you.