Security system at Homes


Nowadays, security at homes is a must for everyone. Since most of the members have there jobs to do, there valuable things like jewelries, cash etc is at risk. To make them secure new products are introduced day by day. But not everyone can afford them. Hence we made this "LASER SECURITY ALARM" which is efficient and cheap.


  1. This project works on interference between a laser and LDR . Place the system in such a place that it is not visible to the thief
  2. Place the two parts on two far ends
  3. When the thief enters the hows and pass through the laser light the alarm stops beeping.

Materials Required

  • 2N5488 NPN Transistor
  • 4.7 kilo ohm Resistor
  • 2.7 ohm resistor
  • LDR (Light Dependent Resistor)
  • 3-12V Siren
  • Laser
  • Wires
  • 9V Battery
  • 9V Battery Clip
  • Printed circuit board


  • First draw the circuit diagram of laser alarm
  • Insert all the components on the PCB
  • Connect positive end of 9V battery clip to one end of buzzer .
  • Connect negative end of the battery to emitter of 2N5488(1) transistor.
  • Connect collector of 2N5488(1) transistor to other end of the buzzer.
  • Connect one end of 2.7 ohm resistor to the base of 2N5488(1) transistor and other to emitter of 2N5488 (2) transistor.
  • Connect the one end of LDR to the negative end of battery clip and other to base of 2N5488(2)transistor.
  • Connect one end of 4.7 kilo ohm to the base of 2N5488(2)transistor and other end to positive terminal of battery.
  • Connct positive end of the battery to collector of 2N5488(2)transistor.

Circuit Diagram


Working of LDR (Laser Dependent Resistor)

  • The Laser light when falls on the LDR electrons crosses the barrier.
  • Hence there is flow of current through the terminals of LDR. and the circuit is complete.


  • But when there is some obstruction between the LDR and the electrons do not flow.
  • The potential difference between the two ends of remains same and do not change.
  • Hence there is no flow of current through the circuit and the alarm does stops beeping.



Project by :

  • Avadh Yadav
  • Atul Mathur
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