The project features a simple red laser and a photocell in order to create a homemade laser security as it involves the use and modification of laser devices. Laser systems operate on the principle that the alarm is activated if the laser is broken and was not received by the photoresistor. A single beam is converted by tiny mirrors discretely placed around the rooms into several beams where a net is formed which will be broken surely by an intruder. The laser system in action is shown in the image below.

From the image below, the laser is attached tightly to the tripod with tape and the laser is kept ON by using rubberband or taping down the power button. For extended life, wires are attached that run to an external battery pack. Also shown are the materials needed to complete the project.

In preparing the receiver, phototransistors are used since they function like microphones wherein they vary the current they allow to pass through them when exposed to changing light levels. Because of this, phototransistors are treated as microphones and they can be attached to the MIC port on a laptop or to the MIC terminals of a preamp and to the input of an amplifier is where the output of the preamp is hooked. The leads of the phototransistor can be screwed right onto the back of the device if a preamp is used. The pins of the phototransistor are taped or soldered to the wires of a stripped headphones chord if laptop is used. The setup is shown in the image below.

When aiming the system, aim the laser at the window while standing by the laser tripod. The reflection of the receiving equipment in the window should be seen. Otherwise, the receiver or laser must be repositioned. The phototransistor will be positioned in the beam once the laser is aimed. The beam can be focused by positioning a magnifying glass in front of the phototransistor. When positioned correctly, most noise from the amp will be heard. The volume on the amp and preamp will need to be adjusted at this point until feedback is heard. The aiming is illustrated below.

Parallel port can be used to control and manipulate the peripheral electronics by assigning to each pin a high or low state. The port can also be controlled over the internet remotely. An external, physical control over software is also possible since the pins can be used as inputs as well.