I've always wondered why the car doesn't warn the driver that there's 100 yards left before it will cut the engine (or limit it to idle), keep the power steering, turn on the hazards, and warn the driver that the vehicle won't continue to function because the key is not in range. Doesn't seem dangerous at all...
That's still dangerous, and it doesn't matter how far out you warn the driver. The moment the car cuts to idle, the driver will lose some control. Imagine this happens while you're in less-than-ideal road conditions and you need to be able to accelerate. And there are a lot of reasons that the key might lose connection to the car other than the 'not present inside the car' case, like for example, the keyfobs battery running out, or the driver dropping their keys into some kind of shielded bag (my car for example has problems sensing the key when it's in an insulated shopping bag that I have).
I think at most you could do something like have the car go into 'limp home' mode if it senses the key was never present in the car for some amount of time after the car is started.
I dropped my wife off downtown in her car and she had the key in her purse. The car did make a weird beeping noise as I drove away, but I had no idea what it meant and I was pulling onto the highway which would have been a bad time for the car to stop driving on me.
I've always wondered why the car doesn't warn the driver that there's 100 yards left before it will cut the engine (or limit it to idle), keep the power steering, turn on the hazards, and warn the driver that the vehicle won't continue to function because the key is not in range. Doesn't seem dangerous at all...