Intruder Alarm

This is a simple single-zone burglar alarm circuit. Its features include automatic Exit and Entry delays and a timed Bell/Siren Cut-Off. It's easy to use. First check that the building is secure and that the green LED is lit. Then move SW1 to the "set" position. The red LED will light. You now have about 30 seconds to leave the building. When you return and open the door - the Buzzer will sound. You then have about 30 seconds to move SW1 to the "off" position. If you fail to do so - the relay will energize and the Siren will sound. While at least one of the switches in the normally-closed loop remains open - the Siren will continue to sound. However, about 15 minutes after the loop has been restored - the relay will de-energize - the Siren will Cut-Off - and the alarm will Reset.

This burglar alarm circuit operates on a simple yet effective design, providing security for a single zone. The circuit is powered by a DC power supply, typically ranging from 9V to 12V, which feeds into the main control unit. The system includes a green LED indicator to confirm that the system is armed and secure.

The user initiates the alarm system by moving switch SW1 to the "set" position, which activates the red LED. This visual cue indicates that the user has approximately 30 seconds to exit the premises before the alarm is armed. During this time, the circuit is monitoring the state of the input switches that form a normally-closed loop, typically comprising door or window contacts.

Upon returning to the building and opening the door, a switch in the loop opens, triggering the buzzer to sound. The user is then given another 30 seconds to return to the control unit and move SW1 to the "off" position. If the user fails to deactivate the system within this timeframe, the relay is energized, and the siren will sound, alerting to a potential intrusion.

The circuit includes a mechanism to ensure that the siren continues to sound as long as at least one switch in the normally-closed loop remains open. This feature provides an ongoing alert until the system is properly reset. After the loop has been restored, the system will continue to monitor the state of the switches. If the loop remains closed for approximately 15 minutes, the relay will automatically de-energize, silencing the siren and resetting the alarm system to its initial state, ready for the next arming cycle.

Overall, this burglar alarm circuit emphasizes user-friendliness and reliability, making it an effective solution for basic security needs. The design can be further enhanced with additional features such as remote notifications or integration with other security systems, depending on the user's requirements.This is a simple single-zone burglar alarm circuit. Its features include automatic Exit and Entry delays and a timed Bell/Siren Cut-Off. It`s easy to use. First check that the building is secure and that the green LED is lit. Then move SW1 to the "set" position. The red LED will light. You now have about 30 seconds to leave the building. When you return and open the door - the Buzzer will sound. You then have about 30 seconds to move SW1 to the "off" position. If you fail to do so - the relay will energize and the Siren will sound. While at least one of the switches in the normally-closed loop remains open - the Siren will continue to sound. However, about 15-minutes after the loop has been restored - the relay will de-energize - the Siren will Cut-Off - and the alarm will Reset.

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