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Alarm zone using normally closed loop (typical)

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Hey All, This is an idea for a multi zone alarm system Im making. This schematic represents just one immediate trigger alarm zone, all others will be basically the same and all zones will latch the relay (electro-mechanical) with reset via a normally closed reset switch to break the line but its not shown here. For purposes of what Im showing you I just wanna be sure it'll work the way I planned and any input is appreciated, everyone does things different. I figured 555 timers and NPN transistors are pretty cheap because its for my home. The door zones will have adjustable time to enter but beyond that time delay will be the same. Any input or advice as always is appreciated.

Operation: The zone return 9V holds the 555 output low and the NPN non conducting, when the zone loop is broken the 1K discharge resistor returns the 555 output to high triggering the NPN and conducting current to the relay sending power to the siren.

Thanks in advance, Jim
 
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