Cut Ignition If Vehicle Is Taken Out Of Park, 2018 Hyundai Elantra

The car is a 2018 elantra and I'm attempting to make a device (relay?) that will allow the car to start but if they try to drive away (put into reverse or drive) it'll shut the engine off. Can someone walk me through how I'd perform something like this please? Thanks!

Three observations:

1) How are you going to disable the device for an authorized driver? (You're asking about a basic "Ghost Switch" installation.)
2) If the vehicle is no longer in PARK, it can be pushed. So even if it can't be driven it can be pushed by hand or another vehicle.
3) If an engine can crank but not start, this will make noise drawing attention to the thief/thieves. Thieves hate making noise. A device that prevents starting makes more noise than one that kills the engine after it starts.

You want the theft attempt to be thwarted before the vehicle is out of PARK. Not after.

Im not really familiar with the Ghost Switch, is that the wireless fuel pump relay kilI? I guess it would be a simple hidden switch for when an authorized user drives. I dont think they would spend that much effort to push the elantra, they are looking for a quick and easy joy ride. Im okay with them drawing attention to themselves. If I have it right in my head, the reverse light would be my relay trigger and when it activates it would cut the ignition circuit. I could put a simple two position switch to prevent that circuit when there is an authorized driver. My concern would be, if they just switched from park to drive, quickly moving pass reverse, would it be enough to still kill the engine.

I could do the wireless fuel pump kill switch like the ghost lock but I dont really like the delay, we were testing them at 5-15 seconds for the car to get the signal and turn off. Let me know what you think about the relay idea above. I know its not really a traditional idea. Thanks!

Ghost Switch refers to a scheme where a system is interrupted and the car won't crank, start, or run. The device is deactivated by pushing an existing switch in the car. I've used horn button, cruise control set button, power seat controls, the cigarette lighter. My Super Duty requires two simultaneous actions. The device arms passively every time you turn off the key and get out. Turn the key on, press the "ghost switch" and the car will start run. The starter signal returns the gohst switch button to its normal operation for the duration of that key cycle.

You can interrupt any circuit you wish. I prefer both the starter and the ECM/PCM turn-on wire. If the ECM isn't powered on, the engine won't start or run. I don't interrupt the fuel pump for the reasons you cite.

There is a simple ghost switch starter interrupt that uses the horn button in the relay section of this site. I've done about a dozen of these now, no two have been identical. This diagram was the schematic that I've developed into subsequent systems. Study this circuit and figure out how it works, and what each relay's function is. Let your mind roam. You'll come up with something.