This is a simple design circuit for alarm circuit. For operates this circuit, we nee a 9VDC battery. But the circuit itself will work from 5 to 15-volts - just choose a buzzer that's suitable for the voltage you're using. The standby current is virtually zero - so the battery life is good. This is the figure of the circuit;
If SW1 is fitted to a door every time the door opens the Buzzer will give a short beep. In an unattended shop - or reception area the sound of the beep will alert you to the fact that you have a customer. How long the output lasts depends on the values of R2 and C2. With the values shown - it will last for somewhere between 3 and 5 seconds. But by increasing these values you can achieve an output time of up to half an hour or more. So if you replace the Buzzer with a relay and use the relay to switch a Siren you have a Simple Intruder Alarm that you can fit almost anywhere. if you replace R2 with a 4M7 resistor you will increase the output time by a factor of about 5. If you replace C2 with a 470uF capacitor you will increase the output time by a factor of about 100. If you use both a 4M7 resistor and a 470uF capacitor together, you will increase the time by a factor of about 5 X 100 = 500. This should give you an output of around half-an-hour or more.
If SW1 is fitted to a door every time the door opens the Buzzer will give a short beep. In an unattended shop - or reception area the sound of the beep will alert you to the fact that you have a customer. How long the output lasts depends on the values of R2 and C2. With the values shown - it will last for somewhere between 3 and 5 seconds. But by increasing these values you can achieve an output time of up to half an hour or more. So if you replace the Buzzer with a relay and use the relay to switch a Siren you have a Simple Intruder Alarm that you can fit almost anywhere. if you replace R2 with a 4M7 resistor you will increase the output time by a factor of about 5. If you replace C2 with a 470uF capacitor you will increase the output time by a factor of about 100. If you use both a 4M7 resistor and a 470uF capacitor together, you will increase the time by a factor of about 5 X 100 = 500. This should give you an output of around half-an-hour or more.
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