Burglar Alarm Circuit

Burglar Alarm Circuit

In this article, I shall list two different burglar alarm  circuits or projects you can easily make. A burglar alarm is basically used to prevent theft/robbery in one’s premises. Burglar alarms can be designed in many ways like the very simple sound alarm, shadow detector alarm to the advanced ones which turn on lights, send SMS alerts,close doors or gate, etc. This is a  fun circuit you can make and also  very useful. In these circuits,  you will  need   buzzers.  It is a component  that  makes  a  buzzing sound when you connect  it  to a  voltage source (battery). The  circuits  are  designed in such a way  the  buzzer will  start  making sound when the  switch  opens or closes.


Simple Burglar Alarm

This is the most basic and cheapest form of burglar alarm. You don’t need to be an electronic genius to make this.The  circuit  is  designed so that  the  buzzer will  start  making sound when the  switch  opens. Switch can be made out  of wires  and  tin foil. For example put some  tin foil  on your door and some  in the  door frame.  And make  sure  they are  touching  when the  door is  closed.  Then  when the door opens, your switch  will  open and sound the  alarm.

Burglar Alarm

Parts List

1. 33k resistor

2. 9V battery

3. Buzzer

4.Any general purpose NPN transistor

5.Switch-You can make that with wires and tin foil or anything that can conduct electricity… Just be creative


Burglar Alarm With Added Components

This circuit is almost the same with the one above. The difference is that SCR (Silicon Controlled Rectifier) also known as Triac is used instead of NPN transistor, capacitor, LED and diode.

How It Works

When the battery is connected, the current flows from the diode to the LED, 470 ohms resistor, buzzer and gets stuck at the “G” at the SCR. Push the PBNO switch (Normally Open Push Button) to activate the buzzer and LED. Before the buzzer and the LED gets activated, the capacitor must be first filled up. The G of the SCR senses the signal when the capacitor is filled and allows current to flow from A (Anode) to the K (Cathode) of the SCR.To reset or stop the alarm push the PBNC switch (Normally Closed Push Button). The capacitor helps to avoid false alarms by preventing any accidental triggering of the SCR.


Parts List

1. 9V battery

2. Diode 1N400X

3. Buzzer

4. 470 and 100k resistors

5. SCR C106B

6. capacitor less than 1μF

7. PBNC switch

8. PBNO switch

Note: First do this on solderless breadboard before transferring it to perforated board.


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