We do understand the urge of keeping our house, work, family safe from intrusions. This project by Ben miller, co-founder of Bluelock.com, guides us how to construct a laser tripwire that buzzes an alarm assoon as the laser is disturbed. This tutorial is based on photo resistor that senses the laser beam and usespiezo to play alarm from an Arduino without an amplifier.

This project requires breadboard, Arduino, 5V General purpose USB charger, Laser chess game mirror, Laser, enclosed piezo element, Breadboard hookup wire kit and Laser mounting stand along with same basic tools like Third hand tool, Computer with Arduino IDE for programming etc. The project uses breadboard and the small wire leads of the laser as well as the piezo element are not breadboard friendly, therefore some rearrangements are done.

The wires are soldered into a short hookup wire to make them attach to the breadboard. Both leads from their respective components are matched to the color of the hookup wire with the color of the lead for consistency. This project uses a Class IIIa laser, which can cause damage to an eye, therefore take extra precautions while dealing with it. The breadboard circuit is assembled based on the following diagram.

The Arduino code in the breadboard is uploaded after with the following steps after the Arduino is attached to the computer with the USB cable and both the lasertripwire.ino and pitches.h files are loaded in the sketch. The tripwire circuit must be pointing the laser at the top of the photo-resistor and the built in LED on pin 13 of the Arduino must light when the laser is positioned on the photo-resistor.