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Make a laser security alarm using light dependent resistor - KT969

Make a laser security alarm using light dependent resistor - KT969


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Transistor BC547



  • connect LDR to the base and emitter of TRANSISTOR
  • connect one side of RESISTOR to base of TRANSISTOR and second one in different rail
  • connect LED Positive to RESISTOR and negative to collector of TRANSISTOR
  • connect positive of BUZZER to RESISTOR and Negative to collector
  • connect RESISTOR to the positive rail of the breadboard with connection wire
  • connect emitter to negative rail of breadboard
  • connect BATTERY 1 positive to Positive rail and negative to negative rail
  • For working of the project , Connect positive and negative of BATTERY 2 to the LASER LIGHT.


Connect the battery the L.E.D and buzzer will come "ON" (if you're in a dark room). Focus the Laser diode/light on the LDR and you will see the L.E.D and Buzzer going "OFF" If you interrupt the laser light focusing on the LDR the circuit will trigger and the alarm will ring!