Hi, want a cheap thief deterrent ? Here is an idea.
1. Buy a 20c L.E.D from JayCar or any electronics store and pick the color and flashing speed of your choice.
2. Buy a 300 ohm resistor and put it on either one of the two legs of the L.E.D
3. Connect the longer leg to 12V+Battery and connect the shorter leg to 12V+Ignition
Done, now when you turn the car off the L.E.D will start to flash, and when you turn the car on, it will stop flashing. All automatic.