Introduction:
Security alarms are an important part of many systems these days. They are designed to indicate the forbidden movements or actions such as prohibited entry at any place or taking any prohibited thing or device. Security alarms systems may use different sensors for different indications like motion sensors, laser light with light sensors, infrared sensors etc.
The laser-based security alarm system is one of the types of security alarm systems that consists of laser light and a light sensor. It basically works by emitting a beam of light in a certain path, if the path of light is broken the change in the output voltage is detected by the detection unit which generates an alarm.
They are effectively used in different buildings and residential apartments for smart monitoring. A simple circuit is explained in this post which uses easily available components to operate.
Component List:
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | NPN Transistor | BC548 | 2 |
| 2. | LDR | – | 1 |
| 3. | Buzzer | – | 1 |
| 4. | LED (Red) | – | 1 |
| 5. | Switch | – | 1 |
| 6. | Resistor | 100Ω | 4 |
| 7. | Battery | 9V | 1 |
| 8. | LDR | – | 1 |
Circuit Diagram:
Laser security alarm can be built using the given circuit diagram:
Construction:
The collector terminal of the transistor Q1 is connected with the buzzer and an LED, while the base terminal gets biased through the collector of the transistor Q2. The LDR is connected to the base of the transistor Q2 through a resistor while the emitter terminal of both the transistors is connected to the 9V battery.
Working Explanation:
The laser light is emitted continuously in a certain path, the laser light falls on the light-dependent resistor and hence LDR delivers low resistance that keeps the transistor Q2 biased by allowing the voltage at its base so that the transistor Q2 remains in ON condition while the transistor Q1 remains OFF. When there is a break in the path of the laser light, the LDR changes its resistance according to it and hence the transistor Q1 gets the supply voltage, and it gets biased which drives the LED and the buzzer indicating the breaking of the path of light.
Applications & Uses:
- Laser security alarms are used to ensure the safety of valuable things and for other security purposes.
- It can act as an additional security alarm for safety lockers in case the security code is hacked.
- It can be used as a boundary wall to check on the babies.
- Furthermore, it can be used at crucial places to make sure no one enters the area.
