hello thanks. i am doing alarm for my auto. here in Bucharest the theef cuts wire to battery and loud sounder.
i am using tranzformer from house supply to 9 volt. my person zaper is 9volt to.but <censored>volt zap.
i am taking zap wire to auto handles and key open entry.
regulater to transistervto switch 9volt than to mos to ignite zap for bad theef. so no need 9volt batery.and person not touch no more my thing.thanks
Hahaha. I've wanted to do something like that as well.
Some words of warning though:
Check with your local laws and a lawyer to ensure that you can't be sued for causing harm for someone touching your auto. This may require a warning sign to be put up.
Additionally, you can use a smaller 12V backup battery in the car, which will still provide 12V to the alarm if the main battery line is cut. The alarm will still go off.
Now.. for the project itself. I would recommend a backup battery anyway, because if the thief cuts the battery wire, there is no way they would leave the cord connected to the house unless it appeared to be a block heater. (This would certainly draw some attention.)
You could wire it so that your 9-Volt device get turned on if the main battery is disconnected.