Regards Luis. I am going to provide you with an anti-theft system due to a power failure for the gasoline or for the central igniter and I tell you my experience in this regard.
I had mounted this same circuit of my invention in a car a few years ago.
At that time the cars did not have as many safety systems as now and being a gasoline engine with conventional carburetion choose to mount a solenoid valve for gasoline which fed with this circuit.
That way I avoided touching the original wiring of the car that was under warranty and in the event that they tried to steal it, it would start but soon it would stop when I consumed the gasoline from the carburetor's gasket and the pockets would be baffled.
The day came when I had to try to steal it and thanks to this circuit they could not take it ..
The circuit is very simple. It has a ground outlet, a positive voltage input that comes from the wrench and a positive output for the motor (solenoid valve or ignition)
When you connect the key, a beep from the piezoelectric buzzer that is in the car's room will sound and you can listen to it, this serves as a reminder to indicate that you have to press the S1 and S2 buttons simultaneously.
I advise you to put a button in a box that simulates a numeric keypad and the other button in a hidden place of easy access.
In this way the eventual caco will think that the anti-theft has a numerical code.
Once you activate it, it remains connected and when you remove the key from the cylinder it is only disconnected, so there is no possibility of forgetting to activate the anti-theft, since you will have to reset it every time you want to start.