circuit help

[polar bear6]

okey, so my friends thinks hes really cool when he takes off the ignition wire on my moped.
(its a Derbi DRD Devil since you really wanted to know http://koti.mbnet.fi/isaksson/senda_r_black_devil.jpg
so i plan to make a anti system with very loud sound, he is a little oversensetiv to sound, he starts yelling that his ears hurt when i clap my hands.
so i when to the store and bought me a rape alarm, its rated 120db so i think he will begin to cry.
i specifically chose a type that you have to pull out a pin because i thought it was like the circuit was broken and the thing started to make sound, i was wrong, and its here i need help.
i need a circuit that turns on when a connection is broken, like the opposite of a transistor.
i don't have time to be fuddling with microcontrollers because the only microcontroller i have a programmer for is a Basic Stamp 2 beginner thing and its to big to put in  my moped
if anyone know how i can do this please tell me.

thx.

[Admin]

you just need an inverter. what an inverter does is take a binary low and makes it a binary high.

this is assuming the ignition always has a high voltage . . . if it doesnt let me know.

ignition -> inverter -> transistor (or mosfet) -> rape alarm -> your friend crying

also, put a small capacitor (or a high value resistor) between ignition and ground. this will pull the ignition line to ground only when the ignition wire is removed, thereby triggering the inverter.

[sdk32285]

Depending on the setup a relay might work. when the coil stops being energized the buzzer rings

[dunk]

yea, but a relay staying closed the whole time would drain the battery overnight.

dunk.
(i think i'm becoming obsessed with battery life...)