Here is the circuit diagram of a very simple wire loop alarm based on  a N-channel enhancement FET 2N700, a buzzer and few passive components.In normal condition the gate of 2N700 (Q1) is connected to the ground through a 100K resistor (R2) and the wire loop. When the wire loop is broken , Q1 will be biased to ON state and the buzzer is activated.The circuit consumes very less standyby current and so the battery will last for a very long period of time.

Circuit diagram.

wire loop alarm circuit


  • Assemble the circuit on a good quality PCB.
  • The circuit can be a powered from a 9V PP3 battery.
  • K1 can be  a  miniature  9V buzzer.


  1. hello sir!!!
    this is quite interesting…….but can u explain its detailed functioning with the explanation on how the wire loop must be made…..
    can n type enhancement MOSFET be used?………..

  2. shweta gupta

    hello sir iam intrested in this project . so can you please expain its working in brief along with the how to use the wire loop section as soon as possible

  3. seetharaman

    Hi a readily available IRF450 can be used. but 2N7000 of Fairchild / Vishay is more suited for this project. BUZ74 can also be used. Any N Channel enhancement mode MOSFET can be used for this project.

  4. what if we couldn’t get the 2N7000? what’s the equivalent/s of this FET? thanks …