Trip Alarm

Hello, i would like to build a circuit, but i do not have enough experience on where to begin. What i want to do is have a circuit that sets off an alarm, however this alarm will be triggered by 2 wires within the circuit. The alarm will only go off if these 2 wires are apart, and it will stay silent when the 2 are together. If what im asking is possible, could you post a schematic?
~Thanks

If it doesn't need to be portable or battery powered you could use a doorbell transformer to power a relay through the trip wire. Using a set of normally closed relay contacts {normally open if the rely is energized} to power the alarm, it would come on if the trip wire was broken.

A quick google search returned this

**broken link removed**

It includes a feature you need, reconnecting the wires does not stop the siren. If the opposite were true a bad guy could just shut the door quickly and minimize attention.

The car horn will have an interrupter with will cause the SCR to turn off, so you'll need to connect a 10k resistor in parallel with the car horn.

Ah ok thanks guys ill try this

Not sure the point of R1/Q1. If you get rid of them.... and move R2, so it's between +12 and the gate.... and connect the top of S1 to the gate....it should work with less components. ( and add Hero's resistor) Or am I missing something?

Ken