Simple Burgler Alarm Circuit

 

The above circuit is a simple Burgler alarm which functions at night and gives out a Buzzer indication when there is an intruder.

• The LDR + 100K combination enables the BC547 transistor only during night
• The collector of BC547 has a PIR sensor connected and powers up only when BC547 is enabled
• The PIR sensor (SR501) provides a output when it detects some motion
• The output of PIR sensor drivers another BC547. A series might be required between PIR output and base of BC547.
• A Buzzer is connected to the collector of BC547 which is activated when BC547 is powered ON