Intruder Alarm

Intruder alarm is very common project for diploma or basic level. Here, by dreamlover technology a verified project on intruder is published, used in door of your house for sound an alarm when anyone open or pushed the door. The circuit of intruder alarm can be used against thieves or intruders.

Circuit description of intruder alarm

The project intruder alarm consist two circuits each of transmitter and receiver separately. Transmitter section comprising a laser diode and power is given from a 9V power supply. Here the receiving section consists of LDR for sensor and work on principle of LDR. When light falling to LDR from laser diode provides base current to transistor T1 which start conducting (but not T2) and the alarm remains off.

When door is pushed, light incident on the LDR is interrupted and it offer high resistance which stop conducting transistor T1 but transistor T2 receive base current and start conducting. The input is given to AND gate N1 from the emitter of transistor T2. Here IC2 work as latch when high output from AND gate N1 is connected to pin 1 and 14 respectively. High output form output pin 12 of IC2 is given to base of transistor T3 through R7 and it cause transistor conduction and consequent sounding of the alarm.

Dreamlover Technology Note: While testing at dreamlover technology Lab, a laser torch in place of the transmitter was used.

anti thief alarm



Resistors (all ¼-watt, ± 5% Carbon)

R1, R2, R6, R8 = 1 KΩ

R3 = 2.2 KΩ

R4 = 10 KΩ

R5 = 100 Ω

R7 = 2.2 KΩ


IC1 (N1) = 7408

IC2 = 7473 JK flip-flop

T1 = BEL187

T2, T3 = SL100


LD1 = Laser diode


9V battery

SW1, SW2 = On/off switch

SW3 = push-to-on switch

Piezo buzzer




Related Project

  1. Wireless Controlled Doorbell controlling range of wireless doorbell is 100M.
  2. 2-Tone Door Bell generates ding-dong sound similar to an electrical bell.
  3. Simple Electronics Siren simple circuit of siren build around single chip CD4011 (IC1)
  4. Melody Doorbell use 3V DC battery to operate instead of AC mains, with good quality sound.
  5. Beeper and Visual Indicator visual indicator lights up with each beep having the same time period.

7 thoughts on “Intruder Alarm”

  1. salam my name is ali raza i didvit ics from punjab college of commerce and now i am in szabist i want to be a software engineer and iam in first semester and InshAllah i will made a door bell and i request please help me safwan alam

  2. Aslm my name is Sanusi saddi muktar from waziri ummaru collage of engineering now I am in electrical engineer my project topic is intruder Alarm,

Leave a Reply

Your email address will not be published. Required fields are marked *