sprocket1597:
What sort of car is it?
A shitty old hilux, just the work pig.
PeterH:
You could wire the ignition switch through a twin throw relay so that when you turn on the ignition switch it turns the Arduino off (and the ignition circuit on), and when you turn the ignition off it turns the Arduino on again (and the ignition circuit off). I recommend putting a switch on the throttle pedal so that the Arduino gets reset if anyone opens the throttle. This means that if anyone sees the running car and tries to drive off, even if they overcome the steering lock it'll die as soon as they try to pull away.By the way, you might want to check the legal situation. In the UK I believe it's illegal to leave a vehicle unattended on a public road with the engine running.
That's actually a really good idea!
And i'm not fussed about legalities - i'm australian, enough said.