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    Here is a simple Anti theft car alarm device for your Car. It generates a loud alarm when there is an attempt of theft. When the intruder opens the door, the circuit senses the attempt of theft and after 2 minutes, the alarm will be activated. The time delay is provided to help the user to leave the car after arming with the device

    The anti theft alarm circuit taps power supply from the car battery. Switch S1 is the on/ off switch of the alarm circuit. When the circuit is activated through S1, the flashing LED blinks indicating that the car is armed. But the alarm generator works only if the Dome lamp of the car is switched on through the door switch. This switch turns on the dome lamp, if any one of the door is opened. The user can put S1 in the on position before leaving the car.

    There will be a delay of 2 minutes so that the alarm will not be generated. When the intruder opens the door, Diode D1 forward biases and capacitor C1 charges through R1. It takes around 1 minute to charge C1. When C1 fully charges, the 12 volt Zener conducts to trigger the NPN transistor T1.Zener diode switch is provided to avoid false triggering and T1 conducts only when C1 charges fully. When T1 conducts C2 charges and the voltage in C2 triggers the gate of SCR. The Horn connected to the Anode of the SCR sounds indicating the theft. The horn can be either a spare car horn or a Hooter that gives loud alarm.

    Anti-theft Car Alarm Circuit diagram

    anti-theft car alarm circuit schematic

    Note: Before leaving the car, switch on S1 and after entering the car switch off S1. Hide S1 in a place that cannot be detected.

    attentionThe author D Mohankumar is not an active member anymore. Please take into consideration that the presented information might not be correct.
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    14 Responses to "Anti-theft Car Alarm Circuit"

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    1. seenivasan says: on July 22, 2010 at 4:45 pm

      Sir,
      i want more projects with diagram please send me my mail.

    2. sagar and sandeep says: on July 22, 2010 at 5:18 pm

      sir…….
      i need more information and diagrams for my collage project…..
      please send me mail…..
      thank you…..

    3. satheesh says: on July 23, 2010 at 1:15 pm

      circuit diagram not viewing

    4. Click on the diagram, you will get enlarged view

    5. musa oluwatobi says: on September 7, 2010 at 9:15 pm

      sir,
      pls i need a more comprehensive report on this particular project( car antitheft alarm) which would help me complete my school project. its a very nice idea and i would like to know if there is anything we can add to make it work better….
      thanks.

    6. sir,
      i need more details regarding this project

    7. sir, i need some simple but attractive projects based on op amp

    8. Sir,i want the pcb layout of this project…

    9. sir…..
      what is the working principle of anti theft car alarm and how it works.?????

    10. I want give detail working principal this project……..please sir
      send to in my mail id………..

    11. Sanchit Chakraborty says: on December 8, 2013 at 6:35 pm

      Sir,
      Please help me to know about the making and working of anti theft car alarm for my nearly coming science exhibition……. Please send me the information to my E-Mail ID…

    12. marjano says: on April 17, 2014 at 9:02 pm

      Thank you very much for so useful imformation.

      I have a car and the wires of the alarm horn pass through the guardmud so thieves that knew this cut the wires , broke the window and opened the trunk taking the spare tire.

      I think this was caused by two design defects of the car:

      1. The trunk switch that can be activated even though the alarm is activated

      2. The horn wires that are easy to reach and be cut by the thieves

      Im making a claim to the car manufacturer and I would like to know if there are any guidelines about how alarms should be designed to be really secure.

      Thanks again

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