Shadow alarms are widely used for security purposes. A shadow alarm is a device that generates an alarm whenever a shadow falls on it. This project can be easily [[wysiwyg_imageupload::]]installed on the windows and doors. This circuit demonstrates the principle and operation of a simple shadow alarm using LDR. Other than the LDR, the circuit consists of LEDs for input and output purposes, buzzer and a LM324 comparator IC. Keep on reading to find out how the circuit is constructed and how it can be made to work.