That's a really cool idea. When I was a kid my data added in immobiliser to our car (flashing LED etc) with a hidden switch. It would have potentially taken quite some time to find if you didn't know where it was.

Adding a puzzle is brilliant and I would love to read a blog about this. Post it here on HN ;)

I’ve seen implementations which need a magnet pressed to the door plastic in a specific place. Security through obscurity as you say but clever anyway - you basically need both a magnet on hand and know where to hold it.

Or time to pull the car apart