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.
1. 33k resistor
2. 9V battery
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.
1. 9V battery
2. Diode 1N400X
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.