How Do You Make A Laser Alarm?
A laser alarm system operates by projecting a beam of invisible laser light across a doorway or window opening. When the light is broken, it activates a buzzer or alarm. The principles are very similar to those of more low tech burglar alarms. A laser alarm requires only slightly more sophisticated electronics and can be put together by anyone with a soldering gun and a knack for tinkering with basic circuits and transistors. Connect a photocell to a 5K resistor. This will pick up the laser light and enable the alarm. Use a 2N3904 transistor to link the resistor, a 1000uF 35v capacitor, a 12v siren and a 9v battery clip. The attached schematic should demonstrate how the parts come together. Use an IC board to hold them in place and make sure the board is small enough to fit into a project box. Do not connect the battery yet. Cut a small hole into the side of the project box big enough to fit the photo cell. Glue a short (1-inch) length of black plastic tube on top of the hole. This wil
