Home security alarm system is a big concern these days. Previously we had published some simple home security systems, the simple burglar alarm system and laser beam alarm circuit are some of them. In this tutorial we will explain how to make a simple wire loop alarm circuit schematics for door security using just four common electronic components: transistor, resistor, buzzer and a battery. It costs around 1$ only. Fixing this home security circuit as door alarms will secure us from intruders.
In this door entry alarm we’ve used a simple wire as door alarm sensor, when someone opens the door it will break the loop and will generate continuous beep sound which won’t stop rapidly. This can be implemented as window alarms too. You can use reed switches as window alarm contacts and alerts can be easily stopped by closing the window, whereas our door system can’t be stopped by closing the door.
Wire Loop Alarm Circuit Schematics
Components for Wire Loop Alarm Circuit Schematics
- Transistor (BC548)
- Resistor (10K)
Working of burglar alarm circuit
- As mentioned before the electronic components used are transistor BC548 (NPN), buzzer and a resistor. Here loop wire is the sensing part of the door alarm system.
- BC548 is an NPN transistor which will be switched ON with a positive voltage on the base terminal.
Here emitter is connected to ground and collector to the negative terminal of buzzer.
- Positive terminal of buzzer is connected to battery positive. When transistor is ON, the buzzer will make beep sound.
- 10K ohm resistor is connected between the base of BC548 and positive terminal of battery, and a loop wire is connected between the base and ground.
- Here loop wire has zero ohm resistance (ideally) and resistor has 10K ohm resistance, so the base has negative potential and transistor will be under OFF condition and buzzer will not make any sound.
- When someone breaks the loop wire, positive potential will reach the base through 10K ohm resistor and transistor starts conducting, then we can hear beep sound until the loop wire is reconnected.
- The door and window alarms system can work on 3V or 9V batteries. Thus it helps to be fixed on the door simply by placing the loop wire in between the door and frame, so as to break it when the door is opened.