Wire Loop Alarm

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 100K 1/2W 1% Resistor R2, R4 2 10K 1/2W 1% Resistor R3 1 1 Meg 1/2W 1% Resistor C1, C3 2 0.1uF Ceramic Disc Capacitor C2 1 0.01uF Ceramic Disc Capacitor IC1 1 4001UBE Quad 2-i/p NOR Gate Q1 1 MPSA14 Low Power NPN Transistor SIREN 1 Micro piezo siren 12V DC 150mA, 110dB @ 1M LOOP 1 See "Notes" MISC 1 Board, Wire, Socket For IC1

Notes

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.