Shock alarm circuit


Here is a simple shock sensitive alarm circuit that has many many applications fro home to automobiles.The main application of this circuit is to use it as an anti theft alarm in automobiles.A peizo electric sensor is used as the shock sensor which has to mounted on the door which you have to protect.

Here the IC1  LM 3558 is wired as an inverting Schmitt Trigger.The POT R1 sets the threshold voltage of the circuit.R1 is used as a feed back resistor.When not activated the out put from the piezo sensor will be low and so do the output of the IC.When the piezo sensor is activated its output voltage goes high and triggers the Schmitt trigger.This results the beeping of the buzzer.The buzzer remains beeping for some time even if the vibration is removed.this is because the increase in the inverting input has little effect when the IC is triggered and the state can’t be easily reversed.

Circuit diagram with Parts list .



  • A 3 v battery can be used as  power supply.
  • Fix the sensor firmly to the surface,where ever you place it.
  • It is always good to place the sensor near to the door knob.
  • Adjust R2 to obtain the required sensitivity.
  • Assemble the circuit on a good quality PCB or common board.
  • Use a IC holder for mounting the IC.
Show Comments

20 thoughts on “Shock alarm circuit

  1. rose

    sir,are all the components required for the circuit available in scrap cfl lamp? if not ,then what all components we need to buy.

  2. Jishnu sravani

    Hi can u please tell me how to get more sound from the buzzer?
    its important please reply me as soon as possible
    thank you

  3. michael

    gud afternun Mr.Seetharaman is it possible 4 dis circuit to use as a mototcycle theft alarm?
    waiting for ur responce….thank you

  4. rajat dhumal

    and make sure that u make use of an expert hand to handle the delicate circuit…or else u’ll be losing hefty bucks…

  5. Seetharaman

    Hi manoharan if a phiezo sensor is stuck on to the door, on the boot, bonnet at suitable location inside. once any body tries to pressure or hit with hammer etc the sensor will produce emf out put. that is further taken care by the above electronics.

  6. Seetharaman

    Hi Elgardo Piezo buzzer is a programmed one will produce only one type of sound / music. sensor / sounder are like solid state loud speakers without any voice coil or cone paper etc.

  7. seetharaman

    Hi friends The shaded wheel is ceramic transducer, the impact sensor. It can be from a old telephone receiver or from any loudspeaker having HF ceramic tweeter. The ceramic tweeter can also be bought in the market as HF transducer with red and black wires connected.

  8. marang thibanyana

    this is nice except that ther is somethin i will need you to forward to my mail. whats that shaded wheel connected to the ic1 LM358 operation amplifier?


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