Simple Door Security Alarm Circuit with Magnetic Reed Switch

Here, in this article, we are going to build an alarm circuit for the door security system. A door security alarm circuit is a simple electronic circuit designed to alert you when a door or window is opened. It's commonly used for home security purposes to notify homeowners of potential unauthorized access. This circuit also can be used in Offices, Apartments, warehouses, and many more.

Here, basically, we have used a magnetic reed switch for this alarming system. The reed switch is a magnetic switch that closes (connects) when it's near a magnetic field and opens (disconnects) when the magnetic field is removed. This is called NO Reed Switch. The NC Reed Switch is also available in the market which opens (disconnects) when it's near a magnetic field and closes (connects) when the magnetic field is removed. The reed switch is generally placed on the door or window frame, while the permanent magnet is placed on the door or window itself.

Circuit Diagram

Here, you can see the circuit diagram of a Simple Door Security Alarm System with a Magnetic Reed Switch.

List of Components

• NO(Normally Open) Reed Switch - 1 PCs
• 9V Buzzer - 1 PCs
• Transistor BC547 - 2 PCs
• LED - 1 PCs
• 100 Kilo-Ohm Resistor - 1 PCs
• 680 Ohm Resistor - 1 PCs
• 22uF Electrolytic Capacitor - 1 PCs
• 9V DC Power Source

Connection Procedure

1. Connect the 100K resistor in series with the 22uF Capacitor across the power supply. Then the middle joint of that resistor and capacitor should be connected to the Base terminal of the first Transistor.
2. Connect the collector terminal of both transistors together.
3. Connect the emitter terminal of the first transistor to the base terminal of the second transistor.
4. Connect the positive terminal of the LED to the positive terminal of the power source in series with a 680 Ohm resistor.
5. Connect the negative terminal of the LED to the Collector terminal of the second transistor.
6. Connect the positive terminal of the Buzzer to the positive terminal of the power source.
7. Connect the negative terminal of the Buzzer to the Collector terminal of the second transistor.
8. Connect the emitter terminal of the second transistor to the negative terminal of the power source.
9. Connect one terminal of the Reed switch to the middle joint of the 100K resistor and 22 uF capacitor and Connect another terminal of the Reed Switch to the negative terminal of the power source.

Operation

When the door or window is in closed condition, the reed switch will be near the permanent magnet, so the reed switch will be closed. As the reed switch is closed the base of the transistor will get a low voltage so the transistor also be in off condition. When the door or window is opened, the magnetic field from the permanent magnet moves away from the reed switch, So the reed switch will be open. And once the reed switch is opened the current start to flow through the transistor and it will get a high voltage. Once the first transistor is activated it will turn On the second transistor. And the second transistor will turn On the LED, and buzzer that activates the alarm.

Read Also: 

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• Fire Alarm Circuit Diagram and Connection Using IC 555
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• Motion Sensing Light Circuit Diagram and Connection Procedure
• Auto Cutoff Lithium Ion Battery (3.7V) Charger Circuit Diagram

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