@Miles
You really know your stuff. I’ve been doing DIY 12V electronics for about 20 years, but I’m not an expert like you. I’ve tested this setup in my own car for a year and feel confident it’s safe. If something goes wrong, they can just swap in the original relay. And the fob battery dying isn’t a big deal either, they can still use the original relay to start the car.
@Cruise
I’ve got 24 years of experience as a Kia dealer tech. A few years ago, my service director came up with a similar system for customers before Kia and Hyundai had updates. His system worked the same but in a different way. It also had a two-button remote, but it disabled ISG and remote start. Customers weren’t happy about that.