Security & Saftey

Pull Pin Security Alarm System

This Pull Pin Security Alarm helps us to get alerted when anybody picks our pockets or bags. The circuit is very helpful to prevent our goods getting pick pocketed. The circuit is called a Pull Pin Security Alarm System because it gets activated as soon as the pin is pulled.


  • Pull Pin Security Alarm System Diagram:
  • Components Required:
  • Description:

Pull Pin Security Alarm Circuit Diagram:

Pull Pin Security Alarm

Components Required:

  • LM380
  • Resistor 1k -3
  • Capacitor 0.1uF-4,250uf-1
  • Speaker-1


The circuit is set up in the following way. The circuit has a pin that is hooked to the pocket and the other end to the circuit. The circuit is inactive until the wallet is in your pocket, and then it is activated when you remove the wallet from your pocket.

Because the pin is hooked to the circuit when the wallet is in the pocket, the circuit remains dormant. When the wallet is taken out of the pocket, the pin is separated from the circuit, and the circuit is triggered. When the circuit is triggered, the small loudspeaker is turned on. An alternating audio frequency signal is supplied into the small loudspeaker.This signal vibrates the loud speaker at an audio frequency so that it is well heard to us.

This can also be used to protect our purses, carry bags, and any other things. The applications of this are not just limited to this but there can be many other applications which you may get on imagining and when you face a problem. The circuit is made to be portable in size so that it can be carried easily with us. It uses a battery power supply.

The oscillator, which generates a sine wave of specified frequency, is the circuit’s main component. The oscillator utilised is an RC phase shift oscillator that generates a sine wave with a specific frequency. The three stages of resistance and capacitance determine the frequency of the RC phase shift oscillator. A 1 K-ohm resistor and a 0.1uF capacitor are used in each stage of the resistor capacitor circuit. Each of these RC phases produces a phase shift of 90 degrees in theory, but in practise, they create a phase change of less than that. They should, on average, create a phase shift of roughly 60 degrees in practise.That is why we have three comparable RC phases, each of which produces a phase shift of around 60 degrees, resulting in a total phase shift of 180 degrees. An additional phase shift of around 180 degrees is produced by the amplifier circuit. As a result, the overall phase shift of the loop is the sum of the phase shifts provided by the amplifier as well as the phase shifts provided by the three RC stages, which total 360 degrees of phase shift.As you all know, this is one of the criterion’s of Barkhausen criterion’s for the circuit to function as an oscillator. The circuit should be provided a voltage of about 6V power supply.

The loud speaker which is used as a load at the output generates sound in audio frequencies. It is a mini loud speaker with an internal resistance of about 8 ohms. When the circuit is activated, the signal from the audio oscillator is fed to the mini loud speaker which then generated a beep sound of that specific audio frequency.


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