This article show how to make a Laser Alarm Circuit for Security which even real spy can use it!
It cost less than big expensive alarm from shop.
Also it is fun to make by ourselves and is good to protect our things.
What is a Laser Alarm Circuit for Security
Laser alarm circuit is small electric system which can know when laser light is broken and make sound alarm.
This type of alarm uses laser beam like fake wall and when someone cross the laser the alarm goes ON.
Main parts of circuit is laser light like laser diode, light sensor like photodiode or LDR, and some small electronic parts.
To make laser beam we use laser pointer and place it in the area we want to protect.
Equation 1: Laser Power (P) = Energy per Photon × Number of Photons per second
We have put LDR sensor light sensor on path of laser beam, it stay inside small dark box with tiny hole so only laser light can pass through it and no other light.
LDR connect to small transistor BC557 using 1 mega ohm resistor.
This transistor help circuit to work correct.
Then we have connected transistor to IC 555 chip at pin 2.
IC 555 is important as it works like timer in monostable multivibrator in alarm circuit.
Pin 3 of IC 555 connects to relay and relay is like small switch for alarm.
When laser is cut the relay turn ON the alarm.
How long alarm sound is OFF depend on resistor R and capacitor C in circuit.
Equation 2: Time Constant (τ) = R × C
Equation 3: Output Time (t) = 1.1 × R × C
How to Build Laser Alarm Circuit:
- First put laser pointer so it shine laser beam across the area we want to protect.
- Then take LDR sensor and put it inside dark box with small hole and put this box right in laser beam path.
- The hole lets laser go in but block other lights.
- Use 1 mega ohm resistor to join LDR to base pin of BC557 transistor.
- Now connect collector pin of transistor to pin 2 of IC 555 and this chip work as timer.
- Then connect relay to pin 3 of IC 555.
- Relay should be connected to alarm wires so when laser is broken the alarm can turn ON.
- To decide how long alarm make sound it uses resistor and capacitor with IC 555.
Parts List:
| Components | Value | QTY |
| Resistors | 10k, 20k 1/4 watt | 1 each |
| 1M | 2 | |
| LDR Standard | 1 | |
| Capacitors | Electrolytic 1000uF 25V | 1 |
| Ceramic 0.22uF, 10nF | 1 each | |
| Semiconductors | IC 555 | 1 |
| Transistor BC547 | 1 | |
| Relay 12V 400Ω | 1 | |
| Diode 1N4007 | 1 |
How It Works:
This simple laser alarm uses laser pointer and LDR light sensor to find if someone enter the area.
When someone block laser beam alarm sound goes on to give alert like security system.
LDR is inside dark box and placed to see the laser beam after it cross the area we want to protect.
Good and Bad of Laser Alarm Circuit:
Good Things:
- Making this laser alarm is cheap way to get more safety.
- We can use it to protect many things like jewelry box, cupboard or full room.
- Not just for safety we can use for school project, science for fun or just time pass project.
Bad Things:
- Laser system not work well in big area as its range is small.
- If something block laser by mistake it can make false alarm.
- Bright light from outside can confuse sensor and make it not work correct.
Conclusion:
This Simple Laser Alarm Circuit for Security is best and easy way for keeping farms and open land safe from unwanted people.
Farmers and land owners can use this DIY system to protect crops and property with more peace of mind.
If anyone have any question or do not understand something feel free to ask in the comment section.
We are happy to help!