Two-Zone Burglar Alarm

This is a two-zone alarm system featuring automatic exit, entry, and siren cut-off timers. It can be activated by standard normally-closed input devices, such as magnetic reed contacts, foil tape, and passive infrared sensors (PIRs). The circuit operates on a 12-volt power supply, but it is compatible with voltages ranging from 9 to 15 volts. Selection of a siren, buzzer, and relay should correspond to the chosen operating voltage. When the switch (Sw1) is moved to the Set position, there is a 30-second window to exit the premises. If re-entry occurs through the Exit/Entry zone, an audible buzzer will activate, allowing another 30 seconds to deactivate the alarm. The Instant zone, however, triggers the siren immediately upon entry, with no delay. After approximately ten minutes of restoring the normally-closed loops, the siren will deactivate, returning the system to standby mode, ready to be triggered again by an intruder. To prevent the siren from sounding a second time, the One-Time-Only Module can be added, which ensures the siren turns off after the first ten minutes and blocks subsequent activation. This module has additional applications worth considering. The timing components are specified in the accompanying diagram, and adjustments to the delay durations can be made by altering the capacitor and/or resistor values; increasing either will extend the delay, while decreasing either will reduce it.

The two-zone alarm system is designed to enhance security in residential or commercial settings by providing flexible and responsive monitoring capabilities. The system architecture includes two distinct zones: the Exit/Entry zone and the Instant zone, each serving specific operational roles. The Exit/Entry zone allows for a grace period when the system is armed, facilitating safe exit and re-entry, while the Instant zone is intended for immediate detection of unauthorized entry.

The circuit utilizes a 12-volt power supply, which can be adjusted to accommodate a range of 9 to 15 volts, ensuring versatility in installation. The selection of components such as sirens, buzzers, and relays must match the voltage level to ensure proper functionality. The inclusion of a switch (Sw1) enables the user to set the alarm, initiating a countdown for exit.

In the event of unauthorized access through the Exit/Entry zone, the system provides an audible alert, prompting the user to deactivate the alarm within a designated time frame. The Instant zone is critical for immediate response scenarios, where any breach triggers the siren without delay, ensuring rapid notification of potential threats.

The system's design incorporates a built-in timer that automatically resets the alarm after a ten-minute period, provided the normally-closed loops are restored. This feature allows for continuous monitoring and reduces the risk of false alarms. The One-Time-Only Module serves as an additional safeguard, ensuring that the siren only activates once within a specified timeframe, thus preventing unnecessary disturbances.

For customization, the timing components are easily adjustable. Users can modify the capacitor and resistor values to change the duration of the exit and entry delays, tailoring the system to meet specific security requirements. This flexibility is essential for accommodating different user preferences and environmental conditions, making the alarm system a robust solution for effective property protection.This is a two-zone alarm - with automatic exit, entry and siren cut-off timers. It can be triggered by the usual types of normally-closed input devices - such as magnetic reed contacts - foil tape - PIRs etc. I`ve used a 12-volt supply in the diagram - but the circuit will work at anything from 9 to 15-volts.

All you need do is select a siren, buz zer and relay to suit the voltage you want to use. When you move Sw1 to the Set position - you have about 30 seconds to leave the building. If you re-enter through the Exit/Entry zone - the buzzer will sound - and you`ll have about 30 seconds to switch the alarm off. The Instant zone has no entry delay. Anyone entering through the Instant zone - will sound the siren immediately. About ten minutes after the normally-closed loops have been restored - the siren will switch off - and the alarm will return to standby mode.

It can then be re-activated by a subsequent intruder. If you don`t want the siren to sound a second time - add the One-Time-Only Module. It forces the siren to switch off after the first ten minutes. And it prevents the alarm from activating a second time. This module has other uses - so it`s worth a look. The various timing components are listed in the diagram. If you want to change the length of any of the delays - change the value of the capacitor and/or the resistor shown. Increasing the value of either - will increases the delay. And reducing the value of either - will shorten the delay. 🔗 External reference