Laser-controlled burglar deterrent:

Since the 1960s, light-emitting diodes (LEDs) have come into use for many applications. Many people may not know that these diodes, used in low-cost laser-pens and laser pointers, were developed for CD players. Today, lasers are used in architecture, in automobile engineering to measure all sorts of part, and in high-precision spirit levels, to name but a few. Lasers are also used in crime fighting, for instance, in highprecision speed traps to catch the unwary, speeding motorist. These are but a few examples of the many applications of lasers. This article describes how a simple laser diode can be used to build an inexpensive burglar deterrent/alarm.