Wire Loop Alarm

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Alex Meaden 206,912 6 27
This circuit is a simple wire loop alarm that can be used in doorways, hallways, or any other place the tripwire will be broken by intruders. The circuit has a built in siren, but it can be replaced by a relay to drive an external siren, commercial alarm, etc.


Schematic for tube amp


Total Qty.
R11100K 1/2W 1% Resistor
R2, R4210K 1/2W 1% Resistor
R311 Meg 1/2W 1% Resistor
C1, C320.1uF Ceramic Disc Capacitor
C210.01uF Ceramic Disc Capacitor
IC114001UBE Quad 2-i/p NOR Gate
Q11MPSA14 Low Power NPN Transistor
SIREN1Micro piezo siren 12V DC 150mA, 110dB @ 1M
LOOP1See "Notes"
MISC1Board, Wire, Socket For IC1


  1. Email Alex Meaden with questions, comments, etc.
  2. The loop can be any type of hookup wire, with a maximum resistance of about 90K. Using very thin wire (40AWG, for example) will make a very sensitive trip wire, but will shorten the distance it can be strung due to the high resistance.
  3. The siren can be replaced with a relay to drive external loads.

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Wire Loop Alarm
Sunday, March 22, 2009 10:43:54 PM
hi i need your help, i picked the wire loop alarm as a project for school and i was just wondering if you can help my by answering some questions that kept me awake for some time and i need technical answers if its not too much trouble. why does the siren stay on when you reconnect the loop and second what are the jobs of the 7th and 14th pin and why are they connected in that way i would really appreciate you answer on this .
Wire Loop Alarm
Friday, November 07, 2008 1:21:39 AM
hi, just wanna ask how long wire this circuit will work? if transistor i change, with kind of what transistor?..thx
Wire Loop Alarm
Tuesday, October 07, 2008 4:59:01 AM
can we replace the siren to a buzzer type and what if we use a solid wire could it be work in this kind of circuit.
Wire Loop Alarm
Friday, August 15, 2008 10:50:53 AM
can we use IC 4002 instead???...plz help!!
Wire Loop Alarm
Saturday, August 02, 2008 2:10:16 AM
Will this work with a 200m or more length of wire loop??
Wire Loop Alarm
Thursday, February 28, 2008 3:48:23 AM
Hey. Thanks for this circuit. I found other loop alarms hard to get working. Can you please send me more information about the alarm. Many Thanks ! Dan
Wire Loop Alarm
Monday, January 14, 2008 10:06:26 AM
which loop should we use is it simple wire loop or which thing is used
Wire Loop Alarm
Wednesday, January 02, 2008 7:51:30 AM
what is the use of the circuit & explain how it works
Wire Loop Alarm
Sunday, November 25, 2007 11:29:51 AM
can u give me the detail?a.s.a.p i think i want to add other circuit.. i want to add autolock circuit.. oh i want to send the signal to my room or other..
Wire Loop Alarm
Wednesday, November 21, 2007 9:19:39 AM
hi there!just wanna ask if you do have the data sheet of each part/material of your wire loop alarm?if so, can you please send it to my e-mail coz i really need those data for our design...hope you can help me...thank you and God bless...
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